Haemoglobin A2

Most laboratories use an upper limit between 3.2 and 3.5 %; low iron lowers the value slightly, so it is best measured when iron is replete; use the range your lab printed.

Adult blood contains mainly haemoglobin A, with a small amount of a second type called haemoglobin A2. The test measures what percentage of the total haemoglobin is A2. The proportion is raised in people who carry beta thalassaemia trait, an inherited change in haemoglobin production that is common in families from the Mediterranean, Middle East, South and South East Asia and Africa.

It is part of the haemoglobinopathy screen. Doctors request it when the red cells are small but iron is normal, in antenatal screening, and when a partner or family member carries a haemoglobin condition.

• Beta thalassaemia trait
• Some other inherited haemoglobin variants
• An overactive thyroid, slightly
• HIV medicines of one class, slightly
• Low vitamin B12 or folate, slightly

• Low iron
• Alpha thalassaemia trait
• Some rare inherited haemoglobin conditions
• Some bone marrow conditions

• Low iron lowers it, which can hide a thalassaemia trait until the iron is corrected
• Different laboratory methods give slightly different values
• A recent blood transfusion changes the proportion

No fasting needed. Interpreted together with the full blood count, ferritin and the rest of the haemoglobin variant screen. Best measured when iron stores are normal.

Written by a UK consultant physician. Typical UK adult reference ranges; your laboratory's own printed range takes precedence.