Haemoglobin A2 (HbA2)

Last updated: Monday, 06, August, 2007

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Item Process
Specimen

5 mL blood in any anticoagulant.

Method

Column chromatography, electrophoresis or HPLC, using lysate of washed red cells.

Reference Interval

1.8-3.5%; check with laboratory.

Application

Investigation of thalassaemias and haemoglobinopathies.

Interpretation

HbA2 is usually raised in the ß thalassaemias, and in unstable haemoglobinopathies where the amino acid substitution is on the ß chain.

Acquired defects of HbA2 also exist. It may also be elevated in thyrotoxicosis and in megaloblastic anaemias. HbA2 may be reduced  in the presence of iron deficiency; if coexistent thalassaemia is suspected the test should be repeated after iron therapy.

It may also be reduced in lead poisoning, anaemia of chronic disease, sideroblastic anaemia, hypothyroidism and in acquired HbH disease.

Reference

Steinberg MH and Adams JG. Blood 1991; 78: 2165-2178.

Bain B. Haemoglobinopathy Diagnosis. Blackwell Science 2001.