HbA2

HbA2 is a minor form of adult hemoglobin, consisting of two alpha and two delta globin chains (α2δ2). In healthy adults, HbA2 makes up about 2-3% of total hemoglobin, with the remaining majority being HbA (α2β2) and a small fraction of fetal Hb (HbF). Its proportion is established after birth and remains relatively stable in adulthood.

The delta globin gene (HBD) is located on chromosome 11, while the alpha globin genes (HBA1 and HBA2) are on chromosome 16. HbA2 is produced in erythroid cells during hemoglobin synthesis as part of the normal maturation of red blood cells. Although its oxygen-carrying properties are similar to HbA, HbA2 has slightly different regulatory characteristics and contributes to overall oxygen transport as a minor component of circulating hemoglobin.

Clinically, HbA2 is routinely measured during hemoglobin analysis to help diagnose and differentiate hematologic conditions. Elevated HbA2 levels (commonly above about 3.5% of total hemoglobin) are a characteristic marker used in the screening for beta-thalassemia trait. HbA2 levels may be normal or reduced in other conditions, such as alpha-thalassemia or iron deficiency, and interpretation should consider the broader hematologic profile. Measurement is typically performed by high-performance liquid chromatography or capillary electrophoresis as part of routine hemoglobinopathy testing.

See also: Hemoglobin A, Hemoglobin F, beta-thalassemia, delta-globin gene.