Lab marker library

Plain-language explanations of every lab marker we cover. Use the cards below as a glossary, or upload your own report and Mediora.AI will walk through each marker in context.

Common lab panels

Complete blood count Lipid panel Metabolic panel Thyroid Iron Liver function Kidney function Diabetes Vitamins Inflammation Hormones Bone health Cardiac markers Electrolytes Adrenal PSA / prostate

↗ Normal reference-range chart (all markers)

Ferritin

Ferritin is the body's main iron-storage protein. A low value usually means iron stores are depleted; a high value can mean inflammation or iron overload.

Hemoglobin A1c (HbA1c)

HbA1c shows your average blood glucose over the last 2–3 months. It is the standard test for diagnosing and monitoring diabetes.

Thyroid Stimulating Hormone (TSH)

TSH is the pituitary's signal to the thyroid gland. It is the single most informative thyroid screening test — high TSH suggests an under-active thyroid, low TSH an over-active one.

Vitamin D (25-OH)

25-hydroxyvitamin D is the storage form of vitamin D and the standard way to measure your vitamin D status.

LDL Cholesterol

LDL ("bad") cholesterol is the cholesterol fraction most directly tied to atherosclerotic cardiovascular disease risk.

Creatinine

Creatinine is a muscle-breakdown waste filtered out by the kidneys. A high level means the kidneys are clearing less than they should.

Fasting Blood Glucose

Fasting blood glucose is the snapshot of your blood sugar after 8+ hours without food — the most basic screening test for diabetes.

Alanine Aminotransferase (ALT)

ALT is an enzyme that leaks into the blood when liver cells are damaged. It is the most liver-specific of the routine "liver function tests".

HDL Cholesterol

HDL is the cholesterol fraction that helps clear excess cholesterol from artery walls. Higher values are generally associated with lower cardiovascular risk.

Vitamin B12 (Cobalamin)

Vitamin B12 is essential for DNA synthesis, red blood cell formation and nerve function. Deficiency causes macrocytic anaemia and neurological symptoms.

Triglycerides

Triglycerides are the body's main form of stored fat. Elevated levels are a marker of metabolic dysregulation and pancreatitis risk.

Aspartate Aminotransferase (AST)

AST is an enzyme released by damaged liver, heart and skeletal-muscle cells. Less liver-specific than ALT but a key part of the routine liver panel.

Read mL/min/1.73m²

Estimated GFR (eGFR)

eGFR is the clinically useful measure of kidney filtration capacity. It is the threshold metric for diagnosing chronic kidney disease.

Total Cholesterol

Total cholesterol is the sum of LDL + HDL + ~20% of triglycerides. It's a coarse marker — the LDL and HDL fractions matter more than the headline number.

Sodium

Sodium is the body's main extracellular electrolyte. Abnormal levels reflect water imbalance more than salt intake.

Potassium

Potassium is the body's main intracellular electrolyte. Both high and low values are arrhythmia risks — every laboratory treats it as critical.

Calcium (Total)

Calcium drives nerve transmission, muscle contraction, blood clotting and bone strength. Levels are tightly regulated; deviations always have a cause worth chasing.

C-Reactive Protein (CRP)

CRP is a liver-made acute-phase protein that rises within hours of any inflammatory stimulus. The most useful general marker of "something is inflamed".

Magnesium

Magnesium is the fourth most abundant cation in the body and a cofactor for 300+ enzymes. Low magnesium is common, frequently missed, and explains many "refractory" potassium and calcium issues.

Bilirubin

Bilirubin is the yellow waste pigment from haemoglobin breakdown. Elevated levels cause jaundice and signal liver, bile-duct or haemolytic problems.

Gamma-Glutamyl Transferase (GGT)

GGT is a bile-duct enzyme — its rise alongside alkaline phosphatase confirms the elevated ALP comes from the liver, not bone.

Uric Acid

Uric acid is the breakdown product of purines. Elevated levels predispose to gout, kidney stones, and (controversially) cardiovascular risk.

Folate (Vitamin B9)

Folate is essential for DNA synthesis and red blood cell formation. Deficiency causes macrocytic anaemia and (in pregnancy) neural-tube defects.

Prostate-Specific Antigen (PSA)

PSA is a glycoprotein made almost exclusively by the prostate. Elevations can mean cancer, benign enlargement, prostatitis or recent ejaculation — the test is sensitive but not specific.

Insulin (Fasting)

Insulin is the hormone driving glucose uptake into cells. A high fasting insulin reflects insulin resistance — the upstream lesion of type 2 diabetes — often years before glucose rises.

Cortisol

Cortisol is the body's primary stress hormone. Both excess and deficiency cause distinct, recognisable clinical syndromes — interpretation is time-of-day dependent.

Albumin

Albumin is the most abundant plasma protein. It carries hormones, drugs and calcium, and maintains osmotic pressure. Low albumin is a sensitive marker of liver synthesis, malnutrition and chronic illness.

Mean Corpuscular Volume (MCV)

MCV is the average size of a red blood cell. It's the most useful single number for classifying anaemia — small, normal, or large.

Red Blood Cell Count (RBC)

RBC is the number of red blood cells per litre of blood. Combined with haemoglobin and MCV, it underpins every CBC anaemia interpretation.

Blood Urea Nitrogen (BUN)

BUN is a kidney-cleared waste product from protein metabolism. Interpreted alongside creatinine; the BUN/creatinine ratio distinguishes pre-renal causes from intrinsic kidney disease.

Alkaline Phosphatase (ALP)

ALP is an enzyme on bone-forming and biliary-duct cells. Elevation can mean liver, bone, intestinal or placental origin — GGT helps tie-break.

Platelet Count

Platelets initiate clotting at sites of vascular injury. Both very low (bleeding risk) and very high (thrombosis risk) values matter clinically — bone-marrow disease, immune destruction or reactive elevation are the leading causes.

White Blood Cell Count (WBC)

WBC is the total leukocyte concentration. The differential — neutrophils, lymphocytes, monocytes, eosinophils, basophils — adds specificity. Always interpret together.

Troponin

Troponin is a structural protein of heart muscle. Elevated blood levels indicate cardiac muscle injury — the cornerstone test for diagnosing heart attack, but other causes exist.

NT-proBNP

Cardiac neurohormone released by ventricular wall stretch. Elevated in heart failure and cardiac stress — the rule-out test for shortness of breath of unclear origin.

Prolactin

Pituitary hormone that drives lactation and is suppressed by dopamine. Elevated outside pregnancy points at prolactinoma, medication effect or stress.

Lipase

Pancreatic enzyme released into blood during pancreatic inflammation. The single most useful test for diagnosing acute pancreatitis — more specific than amylase.

Hemoglobin

Hemoglobin is the oxygen-carrying protein inside red blood cells. A low value defines anaemia.

Amylase

Amylase is a pancreatic enzyme. Sharp elevation (often 3× normal) is the classic biochemical signal of acute pancreatitis.

Lipoprotein(a) (Lp(a))

Lp(a) is a genetically determined LDL-like particle. Elevated Lp(a) is an independent risk factor for early coronary disease, valve calcification and stroke — and is largely unaffected by statins or diet.

Homocysteine

Homocysteine is an amino-acid intermediate whose level rises when B12, folate or B6 are low. Severe elevation is also a marker of cardiovascular and dementia risk.

Free T4 (Free Thyroxine)

Free T4 measures the unbound, biologically active portion of the main thyroid hormone. Together with TSH it pins down whether the thyroid is over- or under-active.

Total Testosterone

Testosterone is the primary male sex hormone (and a smaller-quantity hormone in women). Low values in men cause fatigue, low libido and infertility; high values in women often signal PCOS.

Erythrocyte Sedimentation Rate (ESR)

ESR is a non-specific inflammation marker measured by watching how fast red blood cells settle in a column. Slow but very sensitive to chronic systemic inflammation.

D-dimer

D-dimer is a fibrin breakdown product. A negative result effectively rules out blood clots in low-risk patients; a positive result is non-specific and needs imaging to confirm.

Anti-Thyroid Peroxidase Antibodies (Anti-TPO)

Anti-TPO antibodies attack the enzyme that makes thyroid hormones. They are the marker of autoimmune thyroid disease (Hashimoto's and Graves').

Serum Iron

Serum iron measures iron currently bound to transferrin in circulation. Useful only alongside transferrin/TIBC and ferritin — alone it swings too much to interpret.

Red Cell Distribution Width (RDW)

RDW measures variation in red-cell size. Elevated RDW signals mixed anaemia and — in non-anaemic patients — an independent cardiovascular and mortality risk marker.

Total Iron-Binding Capacity (TIBC)

TIBC measures how much iron the blood could theoretically carry. Together with serum iron and ferritin it pins down iron-deficiency vs anaemia of chronic disease vs iron overload.

Transferrin

Transferrin is the plasma protein that carries iron from absorption sites and storage to the bone marrow. Direct measure of what TIBC estimates indirectly.

Haptoglobin

Haptoglobin is a scavenger protein that binds free haemoglobin released by destroyed red cells. A very low value is the single most sensitive blood marker of haemolytic anaemia.

Free T3 (Free Triiodothyronine)

Free T3 is the active thyroid hormone — three to four times more biologically potent than T4. Useful for confirming hyperthyroidism and tracking specific edge cases of thyroid disease.

Anti-Thyroglobulin Antibodies (Anti-Tg)

Anti-Tg antibodies target thyroglobulin, the precursor protein of thyroid hormones. Complementary to anti-TPO for autoimmune thyroid disease, and clinically critical for thyroid-cancer follow-up.

CA-125

Cancer antigen 125 — best known as a marker for ovarian cancer follow-up. Has many benign causes of elevation and is NOT a screening test in average-risk women.

CA 19-9

Cancer antigen 19-9 — best known for pancreatic cancer follow-up. Often elevated in biliary obstruction or pancreatitis without cancer. About 5–10% of people cannot produce it at all.

Fibrinogen

Fibrinogen is the soluble precursor of fibrin — the protein that physically forms a blood clot. It's also a positive acute-phase reactant, so it rises in inflammation and falls in consumption coagulopathies.

Parathyroid Hormone (PTH)

PTH regulates blood calcium. Always interpreted alongside calcium: high PTH + high calcium = hyperparathyroidism; high PTH + low calcium = secondary response to vitamin-D deficiency or kidney failure.

Reticulocyte Count

Reticulocytes are young red blood cells released early from bone marrow. Their proportion in blood says whether the marrow is RESPONDING to anaemia or has STOPPED making cells.

Activated Partial Thromboplastin Time (aPTT)

aPTT measures the intrinsic + common clotting pathways. The classic test for monitoring heparin therapy and screening for haemophilia and similar factor deficiencies.

Mean Corpuscular Hemoglobin (MCH)

MCH is the average amount of haemoglobin inside a single red blood cell. Tracks tightly with MCV — both fall in iron-deficiency anaemia, both rise in B12 / folate deficiency.

Chloride

Chloride is the body's most abundant negative-charge ion, partnered closely with sodium in fluid balance and stomach acid. It's a routine electrolyte panel marker.

Procalcitonin (PCT)

Procalcitonin is a serum marker that rises rapidly in bacterial infection and sepsis but stays low in viral infection — useful for antibiotic-stewardship decisions.

Aldosterone

Aldosterone is the adrenal hormone that tells kidneys to keep sodium (and water) and dump potassium. Abnormal values explain otherwise unexplained hypertension or potassium imbalance.

Antinuclear Antibodies (ANA)

ANA is a screening test for autoimmune connective-tissue disease — lupus, scleroderma, Sjögren's, mixed CTD. A positive result needs clinical context; many healthy people are also positive.

Growth Hormone (GH)

GH is the pituitary hormone driving growth in childhood and metabolism in adults. Random readings are hard to interpret — the diagnostic tests are GH suppression (for excess) and GH stimulation (for deficiency).

Lactate (lactic acid)

Lactate is a metabolic by-product that rises when oxygen delivery falls behind oxygen demand — a key sepsis, shock and ICU marker. Mildly raised by exercise, severely raised by tissue hypoperfusion.

Insulin-like Growth Factor 1 (IGF-1)

IGF-1 is the liver-produced messenger that does most of growth hormone's downstream work. It's far more stable in blood than GH itself, making it the practical screening test for acromegaly and adult GH deficiency.

DHEA-Sulfate (DHEA-S)

DHEA-S is the dominant adrenal androgen — useful for distinguishing adrenal vs ovarian sources of high androgens in women, and for screening adrenal tumours.

Luteinizing Hormone (LH)

LH triggers ovulation in women and drives testosterone production in men. Paired with FSH, it tells you whether reproductive trouble is at the gland (ovary / testis) or above it (pituitary / hypothalamus).

Follicle-Stimulating Hormone (FSH)

FSH grows ovarian follicles in women and supports sperm production in men. The single best lab marker of ovarian reserve and the workhorse test for menopause.

C-peptide

C-peptide is released 1:1 with insulin when the pancreas makes it, so it measures the patient's own insulin production — the cleanest way to distinguish type-1 from type-2 diabetes and to detect surreptitious insulin use.

Cystatin C

Modern alternative to serum creatinine for estimating kidney filtration rate. Produced at a constant rate by all nucleated cells and cleared only by the kidneys — independent of muscle mass, so more accurate in elderly, frail, paediatric, amputee, bodybuilder and very-thin populations where creatinine misleads.

Read mg/g creat

Microalbumin (urine albumin-to-creatinine ratio)

First-line screen for diabetic and hypertensive kidney damage. Detects albumin leaking through the glomerulus years before serum creatinine moves — the earliest treatable signal.

GAD-65 autoantibodies

The single most useful autoantibody to distinguish autoimmune (type 1, LADA) from non-autoimmune (type 2, MODY) diabetes. Positive titres + low C-peptide is the textbook adult-LADA signature.

Estradiol (E2)

The main and most potent human estrogen. It drives the menstrual cycle, builds the uterine lining, protects bone and blood vessels, and its fall defines menopause. Levels swing enormously across the cycle, so timing the draw is everything.

Progesterone (P4)

The hormone of the second half of the cycle and of pregnancy. A mid-luteal level is the classic proof that ovulation happened. It prepares and maintains the uterine lining and is the most direct blood confirmation of an ovulatory cycle.

Sex hormone-binding globulin (SHBG)

A liver protein that binds testosterone and estradiol and controls how much is biologically free. It is the reason a 'normal' total testosterone can still mean too little active hormone — SHBG is the modifier that makes the number make sense.

Apolipoprotein B (ApoB)

A direct count of the atherogenic particles that cause heart disease. Because every LDL, VLDL and Lp(a) particle carries exactly one ApoB, it measures cardiovascular risk more precisely than LDL cholesterol — especially when triglycerides are high.

Creatine kinase (CK)

An enzyme that leaks out of damaged muscle. It is the main blood test for muscle injury — from ordinary exercise to statin side effects to serious muscle breakdown (rhabdomyolysis), and historically for heart-muscle damage.

Lactate dehydrogenase (LDH)

An enzyme present in almost every cell that leaks out when cells are damaged or turn over rapidly. It is sensitive but non-specific — a raised LDH says 'something is breaking down' without saying where, so it is read alongside more specific tests.

Rheumatoid factor (RF)

An antibody found in most people with rheumatoid arthritis — but also in many healthy older adults and in other conditions. It is a sensitive but not specific screen, best read together with anti-CCP, which is far more specific for RA.

Anti-CCP antibodies

The most specific blood test for rheumatoid arthritis. Unlike rheumatoid factor, a positive anti-CCP rarely appears without RA — and it can turn positive years before the joints, marking people at high risk and predicting more aggressive disease.

Anti-Müllerian hormone (AMH)

The best single blood marker of ovarian reserve — how many eggs a woman has left. Stable across the menstrual cycle, it is used to plan fertility treatment and predict the response to IVF, and it is often high in PCOS.

Hematocrit (HCT)

The percentage of your blood that is red cells. It moves together with haemoglobin and tells the same story — low in anaemia, high in dehydration or when the body over-produces red cells — but is also swayed by how hydrated you are.

Adrenocorticotropic hormone (ACTH)

The pituitary hormone that tells the adrenal glands to make cortisol. Measured together with cortisol, it is the test that separates a pituitary or adrenal problem — the key to working up both cortisol excess (Cushing's) and cortisol deficiency (Addison's).

Phosphate (phosphorus)

A mineral essential for bone, energy and cell membranes, controlled by the same system as calcium — parathyroid hormone, vitamin D and the kidneys. Abnormal levels usually point to a kidney, parathyroid or vitamin D problem rather than diet.

INR (prothrombin time)

A measure of how long blood takes to clot along one of its two pathways. Its main jobs are to monitor the blood-thinner warfarin and to assess the liver's clotting-factor production, since most of those factors are made in the liver.

Non-HDL cholesterol

All the cholesterol carried by artery-damaging particles, in one number — simply total cholesterol minus HDL. It captures more of the risk than LDL alone, needs no fasting, and stays reliable when triglycerides are high.

Renin

The kidney enzyme that starts the hormone cascade controlling blood pressure and salt balance. Measured with aldosterone, it is the test that uncovers primary aldosteronism — the commonest curable cause of high blood pressure.

Bicarbonate (CO2)

The blood's main buffer, keeping its acidity in a tight, safe range. Measured as part of the electrolyte panel, a low or high level signals an acid-base disturbance from the kidneys, lungs, gut or metabolism rather than a problem in itself.

Anti-dsDNA antibodies

An antibody that is highly specific for lupus (SLE) and, unlike a positive ANA, rarely appears without it. Its level often rises and falls with disease activity, especially kidney involvement, so it helps both diagnose and monitor.

Complement C3

A protein of the immune system's complement cascade. In autoimmune disease its useful signal is a LOW level — the proteins get used up when immune complexes form — so a falling C3 often tracks active lupus, especially in the kidneys.

Thyroglobulin (Tg)

A protein made only by thyroid tissue. Its main job is as a tumour marker after treatment for differentiated thyroid cancer: once the thyroid is removed, thyroglobulin should be very low, so a rise can signal returning disease.

Methylmalonic acid (MMA)

A sensitive tie-breaker for vitamin B12 deficiency. When a B12 level is borderline and it's unclear whether the body is truly short, a raised MMA confirms real deficiency at the tissue level — because B12 is needed to keep MMA low.

Neutrophils

The most numerous white blood cell and the body's first responder to bacterial infection. A high count usually means infection, inflammation or stress; a very low count (neutropenia) leaves the body vulnerable to serious infection.

Lymphocytes

The white blood cells of the body's targeted, adaptive immunity — the T cells and B cells that fight viruses and make antibodies. A high count often reflects a viral infection; a low count can follow acute illness, steroids or stress.

Eosinophils

A small subset of white blood cells involved in allergy and in fighting parasites. A raised eosinophil count characteristically points to allergic conditions (asthma, hay fever, eczema, drug reactions) or, worldwide, parasitic infection.

Monocytes

A white blood cell that patrols the blood and matures into a macrophage in the tissues, clearing microbes and debris. A modestly raised count is common during recovery from infection or in chronic inflammation, and is usually a minor part of the blood-count picture.

Total IgE

A blood measure of overall allergic tendency. It reflects how 'atopic' a person is — often raised in allergies, asthma and eczema, and markedly so with parasitic infection — but it does not identify which specific allergy someone has.

Alpha-fetoprotein (AFP)

A protein normally made by the developing fetus and largely switched off after birth. In adults its main use is as a tumour marker for liver cancer and certain testicular and ovarian (germ-cell) cancers, and to monitor treatment.

Carcinoembryonic antigen (CEA)

A protein used mainly to monitor bowel (colorectal) cancer after treatment — a rising level can signal recurrence. It is not a screening test, because it is often normal in early cancer and can be mildly raised in benign conditions and in smokers.

Complement C4

A complement-system protein read together with C3. A low level points to active immune-complex disease — most importantly lupus, where it falls during flares — and a persistently low C4 is a key clue to the rare condition hereditary angioedema.

HE4 (human epididymis protein 4)

A tumour marker used together with CA-125 to estimate the risk that an ovarian mass is cancer. Its advantage is that, unlike CA-125, it is not raised by common benign conditions such as endometriosis and fibroids, making the pair more reliable.

Vitamin B6 (pyridoxine)

A vitamin essential for the nervous system, red-cell production and processing amino acids. Deficiency is uncommon but causes nerve and skin problems and anaemia — and, unusually, taking too much in supplements can itself damage the nerves.

Immunoglobulin A (IgA)

The main antibody protecting the body's surfaces — the gut, airways and other linings. Its most practical everyday use is a supporting one: a total IgA is checked when testing for coeliac disease, because the standard coeliac test can be falsely negative if IgA is low.

Urea

A waste product from the breakdown of protein, cleared by the kidneys. Reported as urea (or as BUN in the US), it reflects kidney function, hydration and protein intake together — so it is always read with creatinine, which is more specific to the kidney.

Immunoglobulin G (IgG)

The most abundant antibody in the blood and the mainstay of long-term immunity — it carries the 'memory' of past infections and vaccinations. A low total IgG can signal an immune deficiency, while a high level often reflects chronic infection or inflammation.

Immunoglobulin M (IgM)

The first antibody the body makes when it meets a new infection, so a raised IgM points to a recent or current one. It is also why 'IgM' antibody tests are used to show an acute infection, as opposed to IgG which shows past exposure.

Fructosamine

A measure of average blood sugar over the previous two to three weeks — a shorter window than HbA1c's three months. It is used mainly as an alternative when HbA1c is unreliable, or to see the effect of a diabetes treatment change sooner.

CK-MB

The heart-muscle fraction of creatine kinase. It was the classic blood test for a heart attack for decades, releasing from damaged heart muscle — but troponin has now largely replaced it as more sensitive and specific. It still has a niche in detecting a second heart attack.

Zinc

An essential trace element needed for immune function, taste and smell, skin, wound healing and hundreds of enzymes. Deficiency causes recognisable problems and is worth correcting, but the blood level is an imperfect guide to the body's true zinc status.

Beta-hCG

The pregnancy hormone — the basis of pregnancy tests. In early pregnancy it rises steeply and predictably, which is used to date a pregnancy and to monitor concerns like ectopic pregnancy or miscarriage. It is also a tumour marker for certain cancers.

Free testosterone

The small fraction of testosterone that is not bound to proteins and is biologically active. It clarifies the picture when the total testosterone is borderline or when SHBG is abnormal — because it is the free hormone that actually acts on the body.

Myoglobin

A protein released from damaged muscle very early, so it rises quickly after injury to heart or skeletal muscle. It is sensitive but not specific, and its biggest clinical role now is in severe muscle breakdown (rhabdomyolysis), where it can harm the kidneys.

Copper

A trace element needed for red blood cells, nerves, connective tissue and many enzymes. Both too little (deficiency, often from excess zinc or malabsorption) and too much (as in the inherited condition Wilson's disease) cause problems, so both directions matter.

Vitamin A (retinol)

A fat-soluble vitamin essential for vision (especially night vision), immune function and healthy skin. Deficiency is rare where diet is good but a major cause of preventable blindness worldwide, and too much from supplements is toxic — so both ends matter.

Vitamin E (tocopherol)

A fat-soluble antioxidant that protects cell membranes and supports the nervous system. Deficiency is uncommon and almost always caused by problems absorbing fat, in which case it can slowly damage the nerves — a treatable cause worth catching.

Vitamin K

A fat-soluble vitamin essential for blood clotting and bone health. Its status is usually judged not by measuring the vitamin directly but by its effect — a deficiency prolongs clotting and raises the INR. It is also the vitamin that warfarin works against.

Ceruloplasmin

The protein that carries most of the copper in the blood and helps handle iron. Its most important use is a low level as a clue to Wilson's disease (copper overload); it also behaves as an inflammation marker, so it rises non-specifically too.

Apolipoprotein A1 (ApoA1)

The main protein of HDL, the 'good' cholesterol that removes cholesterol from artery walls. A higher ApoA1 is generally protective against heart disease, and it is often used with ApoB (the atherogenic-particle protein) as a ratio to gauge cardiovascular risk.

Vitamin B1 (thiamine)

A vitamin essential for turning food into energy and for the nervous system. Deficiency is uncommon on a good diet but important in alcohol excess and malnutrition, where it can cause heart failure or a treatable brain emergency (Wernicke's) — so it must not be missed.

Selenium

A trace element that powers key antioxidant enzymes and helps process thyroid hormone. Deficiency is uncommon where soil selenium is adequate but occurs with malabsorption or long-term artificial feeding; too much from supplements is toxic, so both directions matter.

Vitamin C (ascorbic acid)

A vitamin essential for making collagen, healing wounds, absorbing iron and acting as an antioxidant. Severe deficiency causes scurvy — bleeding gums, poor healing and easy bruising — which is uncommon but still seen in poor diets, alcohol excess and smokers.

G6PD (glucose-6-phosphate dehydrogenase)

An enzyme that protects red blood cells from oxidative stress. When it is deficient — a common inherited condition, especially around the Mediterranean, Africa and Asia — certain triggers (fava beans, some medicines, infections) can make red cells break down, causing sudden anaemia and jaundice.

Ammonia

A waste product from breaking down protein, normally converted by the liver into urea and removed. When the liver is failing, ammonia builds up in the blood and affects the brain, causing confusion (hepatic encephalopathy) — the main reason this test is used.

hs-CRP (high-sensitivity CRP)

A more sensitive version of the CRP inflammation test, able to detect the very low levels of inflammation linked to cardiovascular risk. Used with cholesterol and other risk factors, a persistently higher hs-CRP suggests a somewhat higher long-term risk of heart disease.

Beta-hydroxybutyrate (blood ketones)

The main ketone in the blood, made when the body burns fat instead of glucose for energy. Its key use is in diabetes: a high blood ketone level with high glucose signals diabetic ketoacidosis, a dangerous emergency, so it is measured to catch and monitor that.

Serum osmolality

A measure of how concentrated the blood is — the total dissolved particles per kilogram of water. It is used to work out sodium and water balance problems and, by comparing measured with calculated osmolality (the 'osmolar gap'), to detect certain poisonings such as antifreeze.

Anion gap

A number calculated from your electrolytes that helps make sense of acid problems in the blood. When the blood is too acidic (metabolic acidosis), a high anion gap points to added acids — like the ketones of diabetes or lactate — narrowing down the cause.

Beta-2-microglobulin

A small protein on the surface of most cells that is shed into the blood and cleared by the kidneys. Its main use is in blood cancers, especially multiple myeloma, where the level helps stage the disease and predict outcome — though kidney impairment also raises it.

MCHC (mean corpuscular haemoglobin concentration)

The average concentration of haemoglobin packed inside your red blood cells — in effect, how deeply red each cell is. It is part of the full blood count and mainly helps characterise anaemia: it falls when cells are pale (as in iron deficiency) and is high in a few specific conditions such as hereditary spherocytosis.

Basophils

The rarest type of white blood cell, reported as part of the full blood count differential. Basophils are involved in allergic reactions and inflammation. Their number is normally very low, so the main point of interest is a persistently raised count, which can occasionally be a clue to certain blood disorders.

MPV (mean platelet volume)

The average size of your platelets, reported with the full blood count. Larger platelets tend to be younger and more active, so MPV gives a clue about how the bone marrow is producing them — helping interpret a high or low platelet count.

Transferrin saturation

The percentage of your iron-carrying protein (transferrin) that is actually loaded with iron. It is one of the iron studies and gives a clearer read on iron status than iron alone: a low saturation points to iron deficiency, while a high saturation flags iron overload, as in haemochromatosis.

Tissue transglutaminase IgA antibody (anti-tTG)

The main blood test for coeliac disease. It detects an antibody the immune system makes against a gut enzyme when someone with coeliac disease eats gluten. A positive result in a person with symptoms points strongly to coeliac disease and prompts a confirming gut biopsy.

Faecal calprotectin

A test done on a stool sample that measures inflammation in the bowel. It is most useful for telling inflammatory bowel disease (Crohn's, ulcerative colitis) apart from irritable bowel syndrome, and for tracking how active known bowel inflammation is.

Helicobacter pylori antibody

A blood test for antibodies against Helicobacter pylori, a stomach bacterium that causes ulcers and gastritis. A positive result shows the immune system has met the bacterium, but because antibodies persist after cure, a stool antigen or breath test is preferred to confirm a current, active infection.

Direct (conjugated) bilirubin

The processed fraction of bilirubin, the yellow pigment from the breakdown of red blood cells. When the direct fraction is high, it points to a problem with the liver processing or the flow of bile — such as a blocked bile duct or liver disease — rather than to excessive red-cell breakdown.

Serum free light chains (kappa/lambda ratio)

A blood test that measures the two types of antibody 'light chain' — kappa and lambda — that circulate free in the blood, and reports their ratio. A skewed ratio suggests that a single clone of plasma cells is overproducing one type, which is a clue to myeloma, amyloidosis and related conditions.

Serum protein electrophoresis (SPEP)

A lab test that separates the proteins in the blood into bands to look for an abnormal 'monoclonal' spike — an M-protein. Normally there is no such spike; finding one points toward a plasma-cell disorder such as myeloma or the pre-cancerous state MGUS, and its size is measured in g/L.

TSH-receptor antibody (TRAb / TSI)

An antibody test that confirms Graves' disease — the commonest cause of an overactive thyroid. These antibodies switch on the thyroid's TSH receptor, driving it to overproduce hormone. A positive result pins the diagnosis and helps guide treatment and pregnancy monitoring.

Calcitonin

A hormone made by special 'C-cells' in the thyroid gland. Its main clinical use is as a tumour marker: a raised calcitonin is a signal of medullary thyroid cancer (a rare thyroid cancer arising from these cells), used to help diagnose it and to monitor for recurrence after treatment.

ANCA (antineutrophil cytoplasmic antibodies)

An autoantibody test that helps diagnose a group of small-vessel inflammatory diseases called ANCA-associated vasculitis. A positive result, especially with inflammation and kidney signs, points toward these conditions — but it is always read alongside the clinical picture.

Anti-mitochondrial antibody (AMA)

The signature blood test for primary biliary cholangitis, an autoimmune liver disease. AMA is positive in most people with the condition, so a positive result alongside a cholestatic pattern of raised liver enzymes strongly supports the diagnosis.

17-hydroxyprogesterone (17-OHP)

A steroid hormone made by the adrenal glands, used mainly to diagnose congenital adrenal hyperplasia — an inherited enzyme problem in which 17-OHP builds up. It also features in the work-up of excess male-type hormones in women.

CTX (C-terminal telopeptide)

A blood marker of bone resorption — how fast bone is being broken down. Its main use is in osteoporosis: measured before and during treatment, a fall in CTX shows that a bone-protecting medication is working.

BNP (B-type natriuretic peptide)

A hormone released by the heart muscle when it is stretched or under strain. It is used mainly to help diagnose and monitor heart failure: a low level makes heart failure unlikely, while a high level supports it and tends to track how severe the strain is.

LDL particle number (LDL-P)

A count of how many LDL ('bad cholesterol') particles are in the blood, rather than how much cholesterol they carry. Because it is the number of particles that drives artery furring, LDL-P can reveal higher cardiovascular risk than the standard LDL cholesterol alone in some people.

Remnant cholesterol

The cholesterol carried in triglyceride-rich 'remnant' particles — not LDL and not HDL. Usually calculated for free from a standard lipid panel, it captures an atherogenic, causal contributor to heart disease that LDL cholesterol alone misses, especially when triglycerides are high.

Oxidized LDL (ox-LDL)

LDL cholesterol particles that have been chemically altered by oxidation, making them especially good at inflaming the artery wall and building plaque. A largely research and specialist marker, it reflects the oxidative, inflammatory side of the process behind heart attacks and strokes.

Prothrombin time (PT)

A timed test of how quickly your blood forms a clot through one of its two main pathways. A longer time means clotting is slower. It is the basis of the INR used to monitor the blood-thinner warfarin, and is also a sensitive early sign of liver disease and vitamin K deficiency.

Antithrombin III

One of the body's natural blood thinners — a protein that keeps clotting under control. A low level (antithrombin deficiency), inherited or acquired, tips the balance toward clotting and raises the risk of abnormal clots in veins, so it is tested when someone has an unexplained or unusual clot.

Protein C

A natural anticoagulant — a vitamin-K-dependent protein that helps switch clotting off. A low level (protein C deficiency), inherited or acquired, raises the risk of abnormal clots in the veins, so it is checked as part of investigating an unexplained or unusual clotting tendency.

Protein S

A natural anticoagulant that works as the partner of protein C to switch clotting off. A low level (protein S deficiency), inherited or acquired, raises the risk of abnormal clots in the veins. Pregnancy and some hormones lower it, so timing and interpretation need care.

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Hepatitis B surface antigen (HBsAg)

A protein from the outer coat of the hepatitis B virus. Finding it in the blood means an active hepatitis B infection is present — the virus is there and potentially transmissible. It is the main test used to screen for and diagnose hepatitis B, and to check whether an infection has cleared.

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Hepatitis C antibody (anti-HCV)

An antibody the immune system makes after exposure to the hepatitis C virus. A positive result means the person has been exposed at some point; a follow-up test for the virus's genetic material (HCV RNA) is then needed to tell whether the infection is still present. Hepatitis C is now curable in most people.

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HIV antigen/antibody test (4th generation)

A combined blood test that looks for both a protein of the HIV virus (the p24 antigen) and the antibodies the body makes against it. Testing for both lets it detect infection earlier than antibody-only tests. A reactive screen is always confirmed by a further test before HIV is diagnosed.

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Hepatitis B core antibody (anti-HBc)

An antibody made against the inner core of the hepatitis B virus. Unlike the antibody from vaccination, it only appears after real exposure to the virus, so it marks past or present hepatitis B infection. It is read together with the surface antigen and surface antibody to build the full picture.

Urine albumin-creatinine ratio (UACR)

A urine test that measures how much of the blood protein albumin is leaking into the urine, corrected for how dilute the sample is. A raised ratio is one of the earliest signs of kidney damage, especially from diabetes or high blood pressure, so it is a key screening and monitoring test for kidney health.

Urinalysis (urine test)

A broad first-line urine test that checks many things at once — using a dipstick and, if needed, a microscope — to screen for urinary infection, kidney disease, diabetes and other problems. Rather than a single number, it reports a small panel of findings from a urine sample.

Urine protein (proteinuria)

A measure of how much protein of all kinds is leaking into the urine. Healthy kidneys let very little through, so proteinuria is an important sign of kidney damage; the amount helps show how severe the problem is and is used to diagnose and monitor kidney disease.

Urine specific gravity

A quick measure of how concentrated the urine is — essentially how much dissolved material it carries compared with pure water. It reflects hydration and the kidneys' ability to concentrate urine, and is part of a routine urinalysis rather than a stand-alone test.

Hemoglobin electrophoresis

A test that separates the different types of haemoglobin in the blood and reports each as a percentage. It is the key test for diagnosing inherited haemoglobin disorders — thalassaemia, sickle-cell disease and other abnormal haemoglobins — by revealing which types are present and in what proportion.

Hemoglobin A2 (HbA2)

A minor type of adult haemoglobin, normally making up a small percentage of the total. Its main use is in diagnosing beta-thalassaemia trait, where the HbA2 level is characteristically raised — making it a key part of the haemoglobin analysis.

Direct antiglobulin test (DAT / direct Coombs)

A test that detects whether red blood cells are coated with antibodies. Its main use is to find out whether an anaemia is caused by the immune system attacking the red cells — autoimmune haemolytic anaemia — and to investigate transfusion reactions and haemolytic disease of the newborn.

Reticulocyte hemoglobin (Ret-He)

A measure of how much haemoglobin is packed into the newest red blood cells (reticulocytes). Because it reflects iron supply to red-cell production right now, a low value is one of the earliest signs of iron-deficient red-cell formation — often before the standard iron tests change.

Anti-Ro/SSA antibody

An autoantibody found mainly in Sjögren's syndrome and lupus. It helps confirm these connective-tissue diseases when the symptoms fit, and it has a special importance in pregnancy, where it can affect the baby's heart — so it is checked when these conditions are suspected.

Anti-La/SSB antibody

An autoantibody most often seen in Sjögren's syndrome, and usually alongside anti-Ro/SSA. Adding it helps confirm Sjögren's when dry eyes and dry mouth suggest it. It is rarely found on its own, so it is interpreted together with anti-Ro and the clinical picture.

Anti-RNP (anti-U1-RNP) antibody

An autoantibody found in several connective-tissue diseases. Its standout role is that a high level, together with typical features like Raynaud's and puffy fingers, defines mixed connective-tissue disease — an overlap condition. It is also seen in lupus, so results are read in context.

Anti-Scl-70 (anti-topoisomerase I) antibody

An autoantibody that is highly specific for systemic sclerosis (scleroderma). A positive result in someone with skin thickening and Raynaud's strongly supports the diagnosis and flags a higher risk of lung and kidney involvement, so it helps guide monitoring.

CA 15-3 (breast cancer marker)

A protein shed by some breast cancer cells that can be measured in the blood. It is not a screening test for breast cancer; its main use is to help monitor women already diagnosed with breast cancer — tracking whether treatment is working or the disease is changing over time.

Neuron-specific enolase (NSE)

An enzyme found in nerve and neuroendocrine cells that can rise in the blood with certain cancers, especially small-cell lung cancer and some neuroendocrine tumours. It is a monitoring marker used to follow known disease and response to treatment, not a screening test.

CYFRA 21-1 (lung cancer marker)

A fragment of a structural protein (cytokeratin 19) released by some lung cancer cells into the blood. Its main use is to help monitor non-small-cell lung cancer that is already diagnosed — following treatment response and disease activity over time, not as a screening test.

Squamous cell carcinoma antigen (SCC)

A protein released by squamous cells that can rise in the blood with squamous cell cancers — of the cervix, lung, head and neck, and skin. It is a monitoring marker used to follow known disease and treatment response, not a screening test, and benign skin conditions can raise it too.

Plasma metanephrines

The breakdown products of adrenaline and noradrenaline, measured in the blood. Their main use is to screen for and diagnose a pheochromocytoma — a rare adrenal tumour that pumps out these hormones, causing spells of high blood pressure, headache, sweating and palpitations.

Vanillylmandelic acid (VMA)

A breakdown product of adrenaline and noradrenaline that is passed in the urine, usually measured in a 24-hour collection. Like metanephrines, it is used to look for a pheochromocytoma — a catecholamine-secreting tumour — and to help investigate neuroblastoma in children.

Aldosterone-to-renin ratio (ARR)

A screening calculation that pairs two hormones — aldosterone and renin — to look for primary hyperaldosteronism, an under-recognised and treatable cause of high blood pressure. A high ratio (high aldosterone with a suppressed renin) is the trigger to investigate further.

Reverse T3 (rT3)

An inactive mirror-image form of the thyroid hormone T3. The body makes more of it when unwell, starving or stressed, diverting thyroid hormone away from its active form. It is mainly a marker of serious non-thyroid illness rather than a thyroid test in its own right.

Osteocalcin

A protein made by the bone-building cells (osteoblasts) as they lay down new bone, so its blood level reflects how actively bone is being formed. It is one of several bone-turnover markers used to assess bone metabolism and follow treatment, rather than to diagnose a condition by itself.

P1NP (procollagen type-1 N-propeptide)

The recommended blood marker of bone formation. When bone-building cells make new collagen, they release a fragment called P1NP, so its level reflects how much new bone is being laid down. It is used mainly to check whether osteoporosis treatment is working.

Bone-specific alkaline phosphatase

The bone-made portion of the enzyme alkaline phosphatase, released by bone-building cells. Measuring just the bone fraction gives a cleaner marker of bone formation than total ALP, and it is used especially to assess and monitor Paget's disease of bone.

FGF-23 (fibroblast growth factor 23)

A hormone released by bone that controls phosphate. It tells the kidneys to get rid of phosphate and lowers active vitamin D. It is measured mainly to work out rare phosphate-wasting disorders that cause soft bones, and it rises early in kidney disease.

Vitamin B2 (riboflavin)

A B vitamin the body uses to turn food into energy and to keep other B vitamins working. Deficiency is uncommon on a normal diet and rarely tested directly; when it happens it causes cracked lips, a sore tongue and skin changes, usually alongside shortages of other B vitamins.

Vitamin B3 (niacin)

A B vitamin essential for energy metabolism and for the coenzymes NAD and NADP that run hundreds of reactions in every cell. Severe deficiency causes pellagra — the classic 'three D's' of dermatitis, diarrhoea and dementia. It is rarely measured directly and is usually a clinical diagnosis.

Biotin (vitamin B7)

A B vitamin needed to metabolise fats, carbohydrates and protein. True deficiency is rare. Its biggest practical importance today is the opposite: high-dose biotin supplements (marketed for hair, skin and nails) can distort many other blood tests, including thyroid, hormone and heart-attack (troponin) results.

Iodine (urinary)

An essential trace element the thyroid needs to make its hormones. Too little iodine is the world's leading preventable cause of goitre and hypothyroidism, and is especially important in pregnancy for the baby's brain. Intake is usually judged from a urine iodine level, which best reflects recent intake across a population.

Arterial blood gas (ABG)

A blood test taken from an artery that reads several things at once — the blood's acidity (pH), carbon dioxide, oxygen and bicarbonate. It gives a fast, complete picture of the acid-base balance and breathing, and is used mainly in acutely unwell patients.

Urine sodium

The amount of sodium (salt) in the urine, measured to work out why the blood sodium or fluid balance is off. It shows whether the kidney is holding onto salt (suggesting the body senses low volume) or letting it go, which helps sort out low sodium and some kidney problems.

Urine osmolality

A measure of how concentrated the urine is — the total dissolved particles per kilogram of water. It shows whether the kidney is concentrating or diluting the urine appropriately, which is central to working out low sodium, dehydration and problems with the body's water-controlling hormone.

Base excess

A number calculated from a blood gas that summarises the metabolic side of the blood's acid-base balance. A negative value (a base deficit) means acid has built up or bicarbonate is low — a metabolic acidosis; a positive value means the opposite. It helps judge how severe an acid-base disturbance is.

Inhibin B

A hormone made by the ovaries in women and by the sperm-supporting cells of the testes in men. It reflects how well those tissues are working — used mainly to help assess ovarian reserve in fertility work-up and, in men, testicular sperm production, always read alongside FSH.

Dihydrotestosterone (DHT)

The most potent androgen (male-type hormone), made from testosterone by an enzyme in the skin, hair follicles and prostate. It drives effects such as male-pattern hair loss, unwanted hair growth in women, and prostate enlargement, and is essential for male sexual development.

Estrone (E1)

One of the three main estrogens, weaker than estradiol. Its importance is that it becomes the body's main estrogen after menopause, made in fat tissue rather than the ovaries — so it is used in specialist assessment of estrogen status, particularly in postmenopausal or hormone-related conditions.

Androstenedione (A4)

An androgen (male-type hormone) that serves as a precursor, converted in the body into testosterone and estrogen. Made by both the ovaries and the adrenal glands, it is measured alongside testosterone and DHEAS when investigating the cause of androgen excess, such as PCOS or an adrenal source.

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EBV antibodies (Epstein-Barr virus serology)

Blood tests for antibodies against the Epstein-Barr virus, the usual cause of infectious mononucleosis (glandular fever). The pattern of different antibodies distinguishes a current infection from past exposure — and since most adults have been infected at some point, a positive past-exposure result is very common.

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Cytomegalovirus IgG (CMV IgG)

An antibody test showing whether a person has been infected with cytomegalovirus (CMV) in the past. A positive IgG is very common and usually means past exposure and immunity. Its main practical use is checking immune status before pregnancy, transplant, or when donating blood or organs.

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Toxoplasma IgG

An antibody test showing whether a person has been infected with the parasite Toxoplasma gondii, caught mainly from undercooked meat or cat faeces. A positive IgG usually means past exposure and immunity. It matters most in pregnancy and in people with weakened immunity, where infection can cause harm.

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Rubella IgG

An antibody test that checks whether a person is immune to rubella (German measles), from past vaccination or infection. Its main use is confirming immunity before or during pregnancy, because rubella caught in early pregnancy can seriously harm the developing baby.

Anti-Smith (anti-Sm) antibody

An autoantibody that is highly specific for lupus (systemic lupus erythematosus). It is only found in a minority of people with lupus, so a negative result doesn't rule the disease out — but a positive one, in the right setting, strongly supports the diagnosis.

Anti-Jo-1 antibody

An autoantibody linked to inflammatory muscle disease (myositis) and, importantly, to scarring of the lungs. A positive result in someone with muscle weakness or unexplained breathlessness points to the antisynthetase syndrome and prompts close monitoring of the lungs.

Anti-centromere antibody (ACA)

An autoantibody strongly associated with the limited form of scleroderma (systemic sclerosis), often called CREST. A positive result in someone with Raynaud's and skin changes supports the diagnosis and flags a particular risk of raised blood pressure in the lungs.

Read GPL/MPL U/mL

Anticardiolipin antibody

One of the antiphospholipid antibodies — autoantibodies linked to an increased tendency to form blood clots and to pregnancy complications. A persistently positive result, especially after a clot or recurrent miscarriage, is part of diagnosing antiphospholipid syndrome.

Free PSA (%free PSA)

A refinement of the PSA test. PSA circulates in two forms — bound to proteins and 'free'. The percentage that is free helps tell apart a raised PSA caused by a benign enlarged prostate from one caused by cancer: a higher %free leans benign, a lower %free raises the chance of cancer.

CA 72-4

A tumour marker most associated with cancer of the stomach, and sometimes with ovarian and other cancers. It is not a screening test — its main use is to help monitor a known cancer's response to treatment and to watch for recurrence, alongside other markers and scans.

S100 (S100B)

A protein used as a blood marker in melanoma, the most serious form of skin cancer. It is not a screening test — its main role is to help monitor an advanced or treated melanoma, where a rising level can signal that the cancer is progressing or has come back.

Thymidine kinase (TK1)

An enzyme involved in making DNA, so its level in the blood rises when cells are dividing rapidly. It is used mainly as a marker of activity in certain blood cancers such as some lymphomas and leukaemias — to help gauge how active the disease is and monitor it.

Gastrin

A hormone made in the stomach that drives acid production. It is measured mainly when a rare acid-overproducing tumour (a gastrinoma, causing Zollinger-Ellison syndrome) is suspected — for example with severe or recurrent ulcers — where the fasting level is very high.

Chromogranin A

A protein released by neuroendocrine cells throughout the body. It is the main general blood marker for neuroendocrine tumours (such as carcinoid tumours), used to help diagnose them and to follow the disease — but common things like acid-suppressing medicines also raise it.

5-HIAA (5-hydroxyindoleacetic acid)

The main breakdown product of serotonin, measured in a 24-hour urine collection. Its main use is to detect and monitor carcinoid tumours — neuroendocrine tumours that pour out serotonin and cause flushing and diarrhoea. Certain foods and medicines must be avoided first to avoid false results.

Vasoactive intestinal peptide (VIP)

A gut hormone that, when produced in excess by a rare tumour (a VIPoma), causes profuse watery diarrhoea. The blood test is used when such a tumour is suspected — typically in someone with severe, persistent watery diarrhoea and a low potassium that has no ordinary explanation.

Nucleated red blood cells (NRBC)

Immature red blood cells that still contain a nucleus. They normally stay in the bone marrow, so finding them in an adult's blood is abnormal — a sign the marrow is under heavy demand or stress, from severe anaemia, low oxygen, or a marrow problem.

Immature granulocytes (IG)

Young, not-yet-mature neutrophils that modern blood analysers can count. A small rise usually means the body is fighting an infection and pushing young cells out of the marrow early — a 'left shift'. A larger or persistent rise can point to a marrow disorder.

Methemoglobin

A form of haemoglobin in which the iron has been oxidised so it can no longer carry oxygen. A small amount is normal, but a high level (methemoglobinemia) — usually from certain drugs, chemicals or a rare inherited enzyme deficiency — starves tissues of oxygen and can be dangerous.

Cold agglutinins

Antibodies that make red blood cells clump together when the blood is cold. A low level can be normal, but a high titre can cause 'cold agglutinin disease' — a haemolytic anaemia triggered by cold, sometimes after an infection or linked to a blood disorder.

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Factor V Leiden

The commonest inherited cause of a tendency to form abnormal blood clots. It is a genetic change in clotting factor V that makes it resistant to being switched off, so clotting is harder to stop. The result is reported as present or absent, not a number, and most carriers never have a clot.

Factor VIII

One of the key proteins in the blood-clotting cascade. It matters at both extremes: a low level causes haemophilia A, the classic bleeding disorder, while a persistently high level is a recognised risk factor for abnormal clots. It is measured as a percentage of normal activity.

Von Willebrand factor

A protein that does two jobs in clotting: it helps platelets stick to the wall of an injured blood vessel, and it carries and protects factor VIII in the blood. A low level or a faulty version causes von Willebrand disease, the commonest inherited bleeding disorder.

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Lupus anticoagulant

A confusingly named antibody: despite 'anticoagulant', it actually raises the risk of clotting in the body. It is one of the antibodies of antiphospholipid syndrome, tested after unexplained clots or recurrent miscarriage. The result is reported as present or absent, and needs confirmation on a repeat test.

DHEA (dehydroepiandrosterone)

A weak male-type hormone (androgen) made mainly by the adrenal glands, sitting on the pathway that leads to testosterone and oestrogen. It is measured, usually alongside its longer-lasting form DHEA-S, when working out the source of excess androgens or assessing adrenal function.

Pregnenolone

The 'parent' steroid hormone made from cholesterol, sitting at the very top of the pathway that leads to cortisol, aldosterone and the sex hormones. It is a specialist test, used mainly to help pinpoint an enzyme block in steroid production, such as in certain forms of congenital adrenal hyperplasia.

11-deoxycortisol

The immediate precursor of cortisol — the last step before the body makes its main stress hormone. It is a specialist test used to diagnose a specific form of congenital adrenal hyperplasia (11-beta-hydroxylase deficiency), and in the metyrapone test that assesses the pituitary's reserve.

Thyroxine-binding globulin (TBG)

The main protein that carries thyroid hormone around in the blood. It is measured in specific situations to explain a puzzling thyroid result — when the total thyroid hormone level looks off but the person seems clinically normal, a high or low carrier protein is often the reason.

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Syphilis RPR (rapid plasma reagin)

A blood screening test for syphilis, a sexually transmitted infection caused by the bacterium Treponema pallidum. A reactive result is reported with a titre (a strength) and is always confirmed with a second, specific test; the titre is then used to follow whether treatment is working.

Anti-streptolysin O (ASO)

An antibody the body makes after an infection with group A streptococcus (the 'strep' behind many sore throats). A raised or rising level is evidence of a recent strep infection, used mainly to support a diagnosis of its immune complications — rheumatic fever and a form of kidney inflammation.

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Lyme antibody (Borrelia serology)

A blood test for antibodies against Borrelia, the bacterium behind Lyme disease, which is spread by tick bites. It is done in two tiers — a screening test confirmed by a more specific one — and must be interpreted with symptoms and tick exposure, because antibodies linger after a past infection.

QuantiFERON-TB (interferon-gamma release assay)

A blood test that checks whether your immune system has encountered the tuberculosis bacterium. It is mainly used to detect latent (dormant) TB infection — for example before starting immune-suppressing treatment — and, unlike the old skin test, is not affected by the BCG vaccine.

Lp-PLA2 (lipoprotein-associated phospholipase A2)

An enzyme carried mostly on LDL cholesterol that is produced by inflammatory cells inside the artery wall. Unlike general inflammation markers, it points specifically to inflammation within atherosclerotic plaque, and is used to refine cardiovascular risk beyond standard cholesterol.

Myeloperoxidase (MPO)

An enzyme released by certain white blood cells that generates powerful oxidants. In the blood vessels it promotes inflammation and oxidative damage that destabilise atherosclerotic plaque, so it is studied as a marker of vascular inflammation and cardiovascular risk, used as an adjunct rather than a routine test.

Galectin-3

A protein involved in inflammation and scarring (fibrosis), including of the heart muscle. In heart failure, a higher level reflects ongoing fibrosis and remodelling and is linked to a worse outlook, so it is used mainly as a prognostic marker alongside the natriuretic peptides BNP and NT-proBNP.

Leptin

A hormone made by fat tissue that tells the brain how much energy is stored and helps control appetite. Its level rises with body fat; in obesity it is usually high because the body becomes resistant to its 'I'm full' signal. Rare low levels cause severe childhood obesity.

Fecal elastase-1

A test done on a stool sample that checks how well the pancreas is making its digestive enzymes. Elastase is a pancreatic enzyme that survives passage through the gut, so a low level in the stool signals that the pancreas is not producing enough enzymes to digest food properly.

Fecal occult blood (FIT)

A test on a stool sample that looks for tiny amounts of blood that cannot be seen with the eye. The modern version, the faecal immunochemical test (FIT), specifically detects human blood from the lower bowel, and is a key screening test for bowel (colorectal) cancer and its precursors.

Pepsinogen (I and II)

A blood test that reflects the health of the stomach lining. Pepsinogens are precursors of a stomach digestive enzyme; a low pepsinogen I level and a low pepsinogen I to II ratio suggest the lining has thinned (atrophic gastritis), which raises the long-term risk of stomach cancer.

Anti-endomysial antibody (EMA)

A blood antibody test that is highly specific for coeliac disease. When positive, it strongly supports the diagnosis, so it is used mainly to confirm a positive anti-tTG result. Like anti-tTG, it is an IgA-based test, so total IgA is checked alongside it.

Vitamin B5 (pantothenic acid)

A B-vitamin needed to make coenzyme A, a molecule central to how the body releases energy from food. Because it is present in almost all foods, deficiency is very rare, and this level is measured only in unusual situations rather than as a routine test.

Manganese

A trace metal the body needs in tiny amounts as a helper for several enzymes, including one that protects cells from damage. Dietary deficiency is very rare; the clinically important concern is excess — from industrial exposure or long-term intravenous feeding — which can be toxic to the brain.

Chromium

A trace metal that plays a small supporting role in how the body handles blood sugar with insulin. Dietary deficiency is very rare and hard to prove, and supplements have little proven benefit; blood chromium is measured mainly to check for excess, such as wear from metal joint implants.

Coenzyme Q10 (CoQ10)

A molecule found in nearly every cell that is essential for producing energy inside mitochondria and also acts as an antioxidant. The body makes most of it, so a blood level is measured only in specific situations — such as a suspected inherited deficiency or muscle symptoms on statins — not routinely.

Anti-smooth muscle antibody (ASMA)

An autoantibody directed against components of the body's own smooth muscle (particularly the protein actin). Its main use is in diagnosing type 1 autoimmune hepatitis, where it is a hallmark finding, read together with the antinuclear antibody, a raised IgG and the liver enzymes.

Anti-LKM-1 (liver-kidney microsomal antibody)

An autoantibody targeting an enzyme found in liver and kidney cells. Its defining use is in type 2 autoimmune hepatitis — a less common form of the disease seen especially in children and young adults — where it is the characteristic marker, read with the liver enzymes and IgG.

5'-nucleotidase

A liver enzyme used mainly to answer one question: when the alkaline phosphatase is high, is it coming from the liver or from bone? 5'-nucleotidase rises with liver and bile-duct problems but not with bone activity, so it confirms a cholestatic (bile-flow) source.

IgG4 (immunoglobulin G4)

One of the four subclasses of the IgG antibody. Its main clinical use is in IgG4-related disease — an unusual condition in which IgG4-rich inflammation and scarring affect organs such as the pancreas, bile ducts, salivary glands and others — where a markedly raised level supports the diagnosis.

Urine culture

A test that tries to grow bacteria from a urine sample to confirm a urinary tract infection and identify exactly which bacterium is responsible. It also tests which antibiotics will work (sensitivity), so treatment can be targeted rather than guessed.

24-hour urine protein

A test that measures the total amount of protein leaking into the urine over a full day, collected in one container. It quantifies how much protein the kidneys are losing — an important sign of kidney damage — and defines the heavy 'nephrotic range' loss.

Acetylcholine receptor antibody (AChR)

An antibody that mistakenly attacks the receptors nerves use to signal muscles. It is the hallmark blood test for myasthenia gravis: in someone with fluctuating, tiring muscle weakness, a positive result strongly confirms the diagnosis.

Aquaporin-4 antibody (AQP4-IgG)

An antibody that attacks a water channel on the support cells of the brain and spinal cord. It is the defining blood test for neuromyelitis optica spectrum disorder (NMOSD), a serious condition that can look like multiple sclerosis but is treated differently.

Alpha-1-antitrypsin

A protein made by the liver that protects the lungs from an enzyme that would otherwise break down their delicate tissue. Its key use is to detect alpha-1-antitrypsin deficiency, an inherited condition where a low level leads to early emphysema and, in some, liver disease.

Angiotensin-converting enzyme (ACE)

An enzyme found throughout the body, especially in the lungs. Its blood level is used mainly as a supporting marker in sarcoidosis — an inflammatory condition where the tissue that causes it (granulomas) produces ACE — and to help follow the disease over time.

Read positive/negative

HLA-B27

A genetic tissue type carried by some people. It is not a disease in itself, but it is strongly associated with a family of inflammatory conditions of the spine, joints and eyes — such as ankylosing spondylitis, reactive arthritis and recurrent uveitis — so testing for it supports the diagnosis when these are suspected.

Tryptase

An enzyme stored inside mast cells — immune cells central to allergic reactions. A sharp rise during and shortly after a severe reaction helps confirm anaphylaxis, while a persistently high baseline level points toward mastocytosis, a condition of too many mast cells.

Hepatitis B surface antibody (anti-HBs)

The protective antibody against hepatitis B. It appears after successful vaccination or recovery from past infection, so it is the test used to check whether you are immune to hepatitis B. Unlike most tests, a high level is the good result — it means you are protected.

Measles IgG (measles immunity)

An antibody test that checks whether you are immune to measles. A positive result means you are protected — from a past infection or from vaccination (usually the MMR vaccine). It is used to confirm immunity in healthcare workers, students, travellers and during pregnancy planning.

Calcitriol (1,25-dihydroxyvitamin D)

The active, hormone form of vitamin D, made mainly by the kidneys. This is a specialist test, quite different from the usual vitamin-D blood test — it is measured to work out unusual calcium problems, certain kidney and parathyroid disorders, and some rare conditions, not to check ordinary vitamin-D status.

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Prothrombin gene mutation (Factor II G20210A)

A genetic test for a common inherited change in the prothrombin (Factor II) gene that makes the blood slightly more prone to clotting. It is one of the two most common inherited clotting tendencies (with Factor V Leiden) and is checked when working out why someone had, or is at risk of, a blood clot.