Why is Estimated GFR (eGFR) Low? Causes, Symptoms, and What to Do

A low eGFR means the blood test estimates that your kidneys are filtering blood more slowly than expected. On its own, one low result does not prove kidney disease: chronic kidney disease (CKD) is considered when eGFR stays below 60 for three months, and a single reading can be pulled down by temporary things such as fluid loss, some medicines, a meat-heavy meal or simply age. The most common long-term reasons for a persistently low eGFR are diabetes and high blood pressure, which damage the small blood vessels in the kidneys.

What eGFR measures

eGFR stands for estimated glomerular filtration rate. The glomeruli are the tiny filters in the kidneys. Measuring their filtering speed directly is rarely done, so laboratories estimate it with a formula, usually from blood creatinine (a waste product of muscle) and sometimes cystatin C (another blood protein), together with your age and sex. Kidney health organisations recommend equations that do not include race.

The result is reported in millilitres per minute per 1.73 square metres of body surface area (mL/min/1.73 m²). The same unit is used everywhere; some reports simply write "ml/min".

Check your own value in the calculator above

eGFR ranges and stages

An eGFR below 60 that lasts for three months is considered an indication of CKD. Above 60, CKD is diagnosed only if there is other evidence of kidney damage, most often albumin (a protein) in the urine.

eGFR falls with age, even in healthy people. Average values by age group:

So an eGFR of 75 means something different at 30 than at 75. The formula takes your age and sex into account, and people make different amounts of creatinine depending on their body size and muscle. Labs may flag results differently, so read your number against the range on your own report.

Reasons for a low eGFR

Common long-term causes

• Diabetes – high blood sugar damages the small blood vessels of the kidney filters over years. It is one of the two most common causes of CKD in Western countries.
• High blood pressure – constant pressure damages the same small vessels; it is the other most common cause.
• Ageing – filtering capacity declines gradually, which is why average eGFR is lower in older age groups.
• Heart disease, obesity, smoking and a family history of kidney disease – all raise the risk of kidney damage.

Temporary or "false" reasons

• Fluid loss – vomiting, diarrhoea, bleeding or heavy sodium and fluid loss reduce blood flow to the kidneys. This kind of acute kidney injury often recovers when the cause is treated.
• Medicines – some medicines reduce blood flow to the kidneys or affect creatinine, and iodinated contrast dye used for scans can injure the kidneys. Do not stop any medicine on your own; ask the prescriber.
• Diet – some foods, such as meat, can affect the result, which is why you may be asked to fast or avoid certain foods before the test.
• Unusual muscle mass – creatinine comes from muscle, so very high muscle mass (for example in bodybuilders) can make the creatinine-based result lower than true kidney function. Cystatin C is less affected by muscle mass and may be used instead.

Less common causes

• Glomerulonephritis – inflammation of the kidney filters.
• Polycystic kidney disease – an inherited kidney abnormality with many cysts in the kidneys.
• Blockage of the urinary tract – stones, a blocked bladder or a tumour pressing on the urinary tract stops urine draining.
• Autoimmune disease such as lupus. Frequent urinary tract infections are also a reason doctors keep an eye on eGFR.

What does a high eGFR mean?

A high eGFR is not one of the warning ranges in the staging table (90 or above is the normal range). Estimating equations also become less accurate as the true filtering rate rises. Possible reasons include:

• Pregnancy – the kidneys work harder; the amount of blood they filter peaks between weeks 16 and 24.
• Early diabetes or excess body weight – in the early stage of diabetes, and with obesity, the kidneys can filter faster than normal (called hyperfiltration). This is not a sign of healthy kidneys, and doctors keep monitoring kidney function in these situations.
• Low muscle mass, a limb amputation, frailty, muscle-wasting disease, malnutrition or a vegetarian or low-meat diet – these make creatinine-based eGFR unreliable, so a reassuring number may not reflect true kidney function. A cystatin C test may be used instead.

Symptoms

A low eGFR itself does not cause symptoms. Symptoms belong to the underlying loss of kidney function; they usually develop very slowly, and mild to moderate loss may cause only mild symptoms such as urinating at night. Signs worth reporting include:

• Urinating more than usual, especially at night
• Swelling of the hands, feet or ankles
• Nausea or vomiting
• Dry, itchy or darkened skin, muscle cramps or spasms
• Tiredness (fatigue) and weakness, partly due to anaemia
• Shortness of breath

What usually happens next

1. Repeat the test. A single low value is usually rechecked, because CKD requires a persistently low eGFR over three months.
2. Urine albumin-to-creatinine ratio (uACR). This checks for albumin leaking into the urine, one of the earliest signs of kidney damage. It is reported in mg/g in the US and in mg/mmol in the UK:

A uACR result often needs repeating; a confirmed raised result twice within 3–6 months may mean kidney disease even if eGFR is above 60. 3. Other tests the clinician may order: urinalysis for protein or blood, blood urea nitrogen (BUN), a cystatin C test, a kidney ultrasound or CT scan, and occasionally a 24-hour urine creatinine clearance or a kidney biopsy.

What changes the interpretation: whether the value is stable or falling, your age, muscle mass, pregnancy, recent illness or fluid loss, new medicines, and whether albumin is present in the urine.

Frequently asked questions

What does low eGFR mean? It means your kidneys are estimated to be filtering more slowly than expected for an adult. It may reflect chronic kidney disease, but only if it stays below 60 for three months or other tests show kidney damage. Temporary causes and age can also lower it.

What are the most common reasons for a low eGFR? Over the long term, diabetes and high blood pressure. Short-term reasons include fluid loss from vomiting, diarrhoea or bleeding, some medicines, contrast dye, certain foods such as meat before the test, and unusual muscle mass.

Is an eGFR of 60 bad? An eGFR of 60 falls in the G2 range (60–89). It is not counted as chronic kidney disease unless other tests show kidney damage. Values below 60 for three months meet the definition of CKD. For a person over 70, whose average eGFR is around 75, a value near 60 is not unusual.

Is a low eGFR always a sign of kidney disease? No. A mildly low eGFR does not definitively mean kidney disease, which is why the test is repeated and combined with a urine albumin test before a diagnosis is made.

What does a high eGFR mean? A value of 90 or above sits in the normal range of the staging table. Pregnancy makes the kidneys filter more blood, early diabetes or obesity can make the kidneys filter faster than normal (hyperfiltration), and low muscle mass, an amputation or malnutrition can make the creatinine-based estimate unreliable. If your result is unexpectedly high, your doctor may check it with cystatin C.

Can eGFR go back up? If the cause is short-term, such as fluid loss, the kidneys often recover once the cause is treated, especially when the injury has lasted only a few days. If eGFR stays below 60 for three months, it is assessed as chronic kidney disease, and your doctor can explain what that means for you.

When to see a doctor

If your eGFR is below 60, or lower than in your previous tests, it is worth discussing with your doctor soon so the test can be repeated and a urine albumin test arranged. It is also worth booking an appointment if you have diabetes, high blood pressure or a family history of kidney disease and have not had your kidneys checked. If you notice new swelling of the hands, feet or ankles, or increasing shortness of breath, contact your doctor promptly; severe breathing difficulty or confusion needs urgent care.

Sources

1. Estimated Glomerular Filtration Rate (eGFR) and GFR Tests — MedlinePlus, U.S. National Library of Medicine
2. Estimated Glomerular Filtration Rate (eGFR) — National Kidney Foundation
3. Estimated Glomerular Filtration Rate (eGFR) — Cleveland Clinic
4. Estimated Glomerular Filtration Rate (eGFR) — Testing.com
5. Albuminuria (Proteinuria) — National Kidney Foundation
6. Chronic kidney disease: Diagnosis — NHS
7. Chronic Kidney Disease — Merck Manual Consumer Version
8. Acute Kidney Injury — Merck Manual Consumer Version
9. Physical Changes During Pregnancy — Merck Manual Consumer Version
10. Estimating Glomerular Filtration Rate — NIDDK
11. Clinical Measurements & eGFR Accuracy — NIDDK
12. Glomerular Hyperfiltration in Diabetes: Mechanisms, Clinical Significance, and Treatment — Journal of the American Society of Nephrology (PMC)

Decisions about your health should always be made in consultation with your healthcare provider.