Hemoglobin

Hemoglobin binds oxygen in the lungs and releases it to tissues — a single hemoglobin molecule can carry four oxygen molecules. The blood concentration of hemoglobin, alongside red blood cell count and hematocrit, is the central anaemia work-up: WHO defines anaemia as Hb <13 g/dL in men, <12 g/dL in non-pregnant women, <11 g/dL in pregnant women. The why of low Hb — iron, B12/folate, chronic inflammation, bone-marrow disease, blood loss — needs additional markers to tease apart.

• Men: about 13.5-17.5 g/dL.
• Women: about 12.0-15.5 g/dL.
• Pregnancy: the lower limit falls to around 11 g/dL.
• The WHO anaemia cut-offs are Hb below 13 (men), 12 (non-pregnant women) and 11 g/dL (pregnancy).

Your lab's printed range is what counts.

• Dehydration — concentrates the blood.
• Chronic hypoxia — smokers, COPD, sleep apnoea, high-altitude residence.
• Polycythaemia vera — bone-marrow disorder; usually paired with high platelets and white cells.
• Erythropoietin abuse / certain tumours — rare.

• Iron-deficiency anaemia — most common cause; check ferritin.
• Anaemia of chronic disease — inflammation, kidney failure, malignancy.
• Vitamin B12 / folate deficiency — macrocytic anaemia.
• Acute or chronic blood loss — menstrual, gastrointestinal.
• Hemolytic anaemia — sickle cell, autoimmune.

• Low haemoglobin (anaemia): fatigue, weakness, pale skin, breathlessness, dizziness, cold hands and feet, and sometimes a fast heartbeat.
• High haemoglobin: headache, flushing, itching after a warm shower, dizziness - often from dehydration or chronic low oxygen.
• Mild anaemia can be symptom-free; the pattern of related markers points to the cause.