Medical Encyclopedia › H › Haemoglobin
Haemoglobin (Hb) is the red pigment inside red blood cells. It picks up oxygen in the lungs, carries it to the organs and takes part of the carbon dioxide back on the return journey. To make it, the body needs iron above all.
How is haemoglobin built?
Each haemoglobin molecule consists of four protein chains, each carrying an iron-containing haem group. One oxygen molecule can attach to each of these iron atoms. A small part of haemoglobin is permanently bound to sugar – this fraction is measured as HbA1c and serves as a long-term blood sugar marker.
What values apply?
Haemoglobin is part of every full blood count. Reference ranges depend on the laboratory, age and sex. To classify anaemia, the World Health Organization uses these thresholds for adults:
| Group | Anaemia if Hb is below |
|---|---|
| Men | 13 g/dl (130 g/l) |
| Women (not pregnant) | 12 g/dl (120 g/l) |
| Pregnant women | 11 g/dl (110 g/l) |
Low haemoglobin
A low value means anaemia. The most common cause is iron deficiency, for example from blood loss. Other causes include a lack of vitamin B12 or folic acid, chronic inflammation, kidney disease and increased breakdown of red cells (haemolysis). Typical complaints are tiredness, pallor and breathlessness on exertion.
High haemoglobin
Raised values can result, for example, from dehydration, smoking, longer stays at high altitude, chronic lung or heart disease and the use of testosterone. Less often a bone marrow disorder that produces too many red cells is the cause. A persistently high value makes the blood thicker and should be investigated by a doctor.
Related terms
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- WHO: Guideline on haemoglobin cutoffs to define anaemia in individuals and populations (2024)
- Onkopedia guideline Iron deficiency and iron deficiency anaemia (DGHO, Germany)
- German Medical Association guideline on quality assurance in laboratory medicine (Rili-BÄK)
This entry is for general information only and does not replace medical advice. Last updated: November 2026.