Hb A2 in Subjects with Hb D

Dr. Huisman’s paper on “Combinations of β chain abnormal hemoglobins with each other or with β-thalassemia determinants with known mutations: influence on phenotype” (1), was of great interest to us because Bahrain has a high prevalence of hemoglobinopathies (2). Monitoring with cation-exchange HPLC (Bio-Rad Variant) was started in 1997, and 11 800 blood samples were screened in that year. According to Dr. Huisman, when “a slowly moving variant like Hb D was present, the Hb A2 zone was often contaminated with small amounts of minor (modified) Hb D, resulting in Hb A2 values that were too high”. Our results in 27 cases of Hb D trait do not agree with this. The median value for Hb A2 was 1.6% (range, 0.9–2.5%) in Hb D trait cases against a median value of 2.6% (range, 1.7–3.1%) in healthy subjects (Table 1). Low Hb A2 was also seen in Hb S-D disease cases. Our data agree with the fact that, in the presence of sickle hemoglobin, the Hb A2 peak is inappropriately high [as noted in the Bio-Rad application note and also observed by Wild and Stephens (3)]. Thus, when Hb D-B thalassemia cases are interpreted, Hb A2 values should be interpreted as in the β-thalassemia trait. The reason for low Hb A2 in Hb D cases is unclear. A portion of Hb A2 in these cases may elute with either the A or D peak, or the mutation itself may influence the amount of delta chain, because its expression is low even in Hb S-D. Hb A2 concentrations in healthy subjects and HbD, HbS, and β-thalassemia trait cases. Hb A2 concentrations in healthy subjects and HbD, HbS, and β-thalassemia trait cases. Titus H. J. Huisman Department of Biochemistry, and Molecular Biology, Research & Education Building, Room CB-2208, Medical College of Georgia, Augusta, GA 30912-2114, Fax 706-721-3092 Thank you for sending me the short note by Dr. Dash. She is probably correct that quantification of Hb A2 with her HPLC system in Hb D-Punjab-containing samples is different from that observed earlier in my laboratory; it shows how different the results can be with different columns and/or elution systems. It would be interesting to see if the Hb A2 concentrations in her Hb D-containing samples are again on the low side of normal when analyzed with other procedures (DEAE-cellulose chromatography or cellulose acetate elution procedure).