The importance of hemoglobin A2 determination☆

Hemoglobin (Hb) A2 ( 2 2) constitutes less than 3% of the total hemoglobin (Hb) in adults and has almost no physiological importance.1 On the other hand, the determination of Hb A2 is an important tool to diagnose the beta-thalassemia trait (BTT).1,2 Although individuals with BTT do not need treatment, the accurate detection of the carrier state is important in genetic counseling to determine risk of having a child with a major disease.3 Elevated levels of Hb A2 and microcytosis are suggestive of the diagnosis of BTT. However, BTT may be present with normal levels of Hb A2 as a few cases of -thalassemia are not associated with elevated Hb A2, and because of the association of BTT with iron deficiency or with -thalassemia ( -Thal).1,2,4–6 There are many other factors, inherited or acquired, that can interfere in Hb A2 levels (Table 1).3,4 Hb A2 can be measured by several laboratorial methods, but these methods have differences in accuracy.7 Cation exchange high performance liquid chromatography (HPLC), microcolumn chromatography, and cellulose acetate electrophoresis with elution are considered acceptable methods to diagnose BTT, whereas cellulose acetate electrophoresis followed by scanning densitometry is not.2 The accuracy of cellulose acetate electrophoresis with elution depends on the training and experience of the laboratory technician who performs