Biomarker · Blood cells

Haemoglobin

Also known as: Hb, hemoglobin, haemoglobin concentration

The iron-containing protein inside red blood cells that carries oxygen from the lungs to every tissue. Its concentration is the standard measure of anaemia and the first number read on a full blood count.

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Also known as
Hb, hemoglobin, haemoglobin concentration
Units
g/L in the UK, g/dL in the United States (1 g/dL = 10 g/L)
Measured by
Full blood count

What it is and what it does

Each red cell is packed with haemoglobin, a four-part protein whose iron atoms bind oxygen in the lung capillaries and release it where oxygen is low. The concentration in blood reflects the balance between production in the bone marrow (which needs iron, vitamin B12, folate and the kidney hormone erythropoietin) and loss or destruction of red cells. A low value is anaemia; the size of the red cells (MCV) then points to the cause.

Why it may be higher

  • Living at altitude, smoking and chronic lung disease (the body makes more red cells when oxygen is scarce)
  • Dehydration, which concentrates the blood
  • Polycythaemia vera and other bone-marrow disorders
  • Testosterone and erythropoietin treatment

Why it may be lower

  • Blood loss: heavy periods, bleeding from the gut, surgery or injury
  • Iron, vitamin B12 or folate deficiency
  • Chronic kidney disease (too little erythropoietin) and long-term inflammatory disease
  • Haemolysis, inherited haemoglobin disorders (thalassaemia, sickle cell disease), bone-marrow failure
  • Pregnancy, where plasma volume expands faster than red-cell mass

A high or low value can be associated with several different situations. The result is interpreted with other results, symptoms, history and clinical findings.

What can affect the result

  • Pregnancy and the menstrual cycle
  • Fluid balance at the time of sampling
  • Recent transfusion or blood donation
  • Sex, age and altitude of residence, which change the reference interval
Reference ranges. Reference intervals for this marker depend on the laboratory, the assay, the units, age, sex and pregnancy. Interpret a result against the interval printed on the laboratory report, not against a figure from the internet.

Medicines that can change it

AspirinIbuprofenOmeprazole

Each medicine page lists its effect on this marker under "Effects on tests and results", with the source.

Educational content. A biomarker page explains what a substance is and why its level can change. It cannot determine the cause of your result: interpret a result using the range supplied by the laboratory that performed the test, with the clinician who ordered it.