Higher sensitivity of capillary electrophoresis in detecting hemoglobin A2'compared to traditional gel electrophoresis.

HbA2' (also called Hb B2) is the most common delta-globin chain defect and is reported to occur in 1-2% of the African American population. The major clinical significance of HbA2' is that the failure to detect it might lead to an underestimation of the total HbA2, leading to failure to diagnose β-thalassemia minor. In order to diagnose β-thalassemia minor, both HbA2 and HbA2' levels must be combined.Hb A2' accounts for a small percentage (1-2%) of the total hemoglobin in heterozygotes. It is difficult to detect this small amount by traditional gel electrophoresis. Using HPLC Hb A2' is easily detected as it produces a minor peak in the S window. Other conditions which might interfere with detection of HbA2' by HPLC include Hb S trait or Hb SS disease (Hb A2' hidden in the S peak), transfused Hb SS (Hb S peak may be very small), Hb C trait or Hb CC disease (glycosylated Hb C elutes in the S window), and Hb G (Hb G2 elutes in the S window). All of the above conditions, including Hb A2', occur most commonly in the same ethnic group (African American). We reviewed 654 consecutive cases over a period of three months for the presence of Hb A2' in our laboratory where capillary electrophoresis is used as the primary diagnostic tool. We detected seven cases (1.07 %) of HbA2'. In contrast, we did not detect any HbA2' using conventional gel electrophoresis in the last one year (2,580 cases). Although in none of the seven cases the sum of Hb A2 and Hb A2' exceeded 3.5%, we believe that capillary electrophoresis allows for a better detection of Hb A2' than gel electrophoresis and HPLC.