What it measures
The test looks at the types of haemoglobin, the protein in red blood cells that carries oxygen. It picks up variants such as haemoglobin S (sickle cell) and measures the forms that point to beta thalassaemia. The result shows whether someone carries a trait or has one of these conditions.
Why people test it
- Offered in pregnancy to see whether a baby could inherit sickle cell disease or thalassaemia.
- Taken before starting a family to find out carrier status.
- Used when a blood count shows small red cells but iron levels are normal.
Typical range
There is no single range. The report lists the haemoglobins found and says whether a trait or condition is present, in the lab's own wording. Alpha thalassaemia trait often cannot be confirmed this way and may need a DNA test.
Finger-prick or vein?
A vein sample is usually advised, because the lab needs a tube of whole blood that has not clotted.
A blood transfusion in the previous few months can make the result unreliable, as the donor's haemoglobin is in the sample.