Hemoglobin A2 (HbA2)
A minor type of adult haemoglobin, normally making up a small percentage of the total. Its main use is in diagnosing beta-thalassaemia trait, where the HbA2 level is characteristically raised — making it a key part of the haemoglobin analysis.
What it measures
HbA2 is a minor form of adult haemoglobin, normally accounting for a small fraction (about 2–3%) of the total. It is measured as part of haemoglobin analysis (electrophoresis or HPLC), and its main value is a specific one: the level of HbA2 is the classic marker for beta-thalassaemia trait. Beta-thalassaemia is an inherited condition in which one of the haemoglobin chains is underproduced; in the carrier (trait) form, the body compensates in a way that raises HbA2, typically above about 3.5%. So when someone has a long-standing mild anaemia with small red cells (a low MCV) that iron deficiency does not explain, a raised HbA2 points to beta-thalassaemia trait as the cause. The level is interpreted carefully, because iron deficiency can lower HbA2 and mask a trait, while some conditions can affect it in the other direction. HbA2 is therefore not a general screening number but a specific piece of the picture used to confirm or exclude beta-thalassaemia trait alongside the blood count and the rest of the electrophoresis.
What a high value can mean
- Beta-thalassaemia trait — the classic cause; HbA2 raised above about 3.5%.
- Note on interpretation — coexisting iron deficiency can falsely lower HbA2, so iron status is checked alongside it.
What a low value can mean
- Normal — a low-normal HbA2 within a normal blood count is unremarkable.
- Iron deficiency — can lower HbA2 and potentially mask a beta-thalassaemia trait; iron studies help interpret this.
- Certain alpha-thalassaemias — may show a low or low-normal HbA2.
When to discuss with a doctor
HbA2 is a specific diagnostic marker rather than a number to act on directly. It is measured when a persistent microcytic anaemia is being investigated and iron deficiency has been considered, to confirm or exclude beta-thalassaemia trait. A raised HbA2 supports the trait, which usually causes only a mild anaemia and needs no treatment in itself — but knowing about it matters for genetic counselling, because if a partner also carries a haemoglobin trait there is a risk of a more serious condition in a child. Because iron deficiency can distort the HbA2 level, it is always read together with iron studies and the blood count. Mediora.AI can show HbA2 alongside the MCV, haemoglobin and iron markers so the thalassaemia pattern is visible; confirming the diagnosis and any counselling belong with your doctor.