Hemoglobin A2

Hemoglobin molecules are composed of two pairs of globin chains each containing a heme group at its core. The heme group is where the exchange of oxygen and carbon dioxide occurs.

Shortly before birth, a switch occurs that shuts off the production of gamma globin chains by most erythroid cells and begins synthesis of beta and small amounts of delta globin chains. This results in the production of adult hemoglobins A and A2. Hemoglobin A is composed of two alpha and two beta globin chains, while hemoglobin A₂ is composed of two alpha and two delta globin chains. The level of Hb A₂ increases gradually through the first year of life at which time adult levels are reached.

HbA2 levels are decreased or at the lower end of the normal range in patients with alpha thalassemia minor. Elevated levels (7-8%) of Hb A₂ are seen in patients with beta thalassemia minor. Several abnormal hemoglobins including Hb S, E, C and O may cause spurious elevation. To avoid misinterpretation, hemoglobin electrophoresis should be run on all samples. Hb A₂ may be increased with megaloblastic anemia and decreased with iron deficiency anemia. 

Hemoglobin A2 levels are determined by hemoglobin electrophoresis. The adult reference range is 2.3-3.5%. 

Specimen requirement is one lavender top (EDTA) tube of blood.

References

Zhaohai Y, et al. Prevalence of Elevated Hemoglobin A₂ Measured by the CAPILLARYS System, Amer J Clin Path, 2009;131(1):42–48.

Giambona A, et al. The significance of the hemoglobin A2 value in screening for hemoglobinopathies, Clin Biochem, 2009;42(18):1786-1796.