Haemoglobin (Hb) blood test: normal range

Haemoglobin measures the amount of this oxygen-carrying protein in your blood, usually in g/dL. MedlinePlus says the level gives information about the health of your red blood cells, and Testing.com describes the test as a check of the blood's oxygen-carrying capacity. It is almost always reported as part of a complete blood count (CBC or CBP).

The haemoglobin test is not the same as HbA1c, which checks average blood sugar. Reports often spell it Hemoglobin, Hb or HGB, and some print it in g/L, where 13.8 g/dL becomes 138 g/L.

Doctors most often order haemoglobin to check for anaemia, when the body does not have enough healthy red blood cells, and to follow its treatment. MedlinePlus lists weakness, dizziness and cold hands and feet among the symptoms, along with a family history of thalassaemia or sickle cell anaemia, a diet low in iron, long-term infection and heavy blood loss.

The test is also used to look for too many red cells, to monitor long-term kidney disease or chemotherapy, and before surgery. WHO defines anaemia as haemoglobin below a cut-off that depends on age, sex and pregnancy: at sea level, below 120 g/L (12.0 g/dL) for non-pregnant women and below 110 g/L for pregnant women.

Haemoglobin changes with things that are not illness, and the reference range itself shifts with age and sex.

• Living at high altitude raises haemoglobin for several weeks, because the air carries less oxygen.
• Smoking raises it; dehydration, as after severe diarrhoea, concentrates the blood and raises it too.
• Pregnancy lowers it, because plasma volume grows faster than red cells, so a slightly low second-trimester value can be normal.
• Heavy menstrual periods, injury or surgery lower it through blood loss.
• Too little iron, folate or vitamin B12 lowers it over time; iron supplements, chemotherapy and some antibiotics change red cell production.
• Diet, activity level and some inherited conditions can affect the result, and the range differs by lab, age, race and sex.