Chromatographic measurements of memoglobin A2 in blood samples containing sickle hemoglobin.

Letter to the Editor We would like to comment on the article by Shokrani et al [ 1 ], published in the April 2000 issue of the Annals o f Clinical & Laboratory Science. The authors begin their abstract by stating that HbA2 measurements aid in the differential diagnosis of sickle cell anemia from sickle-beta-thalassemia. This, unless meant for the analysis of families, is incorrect. The HbA2 value is of no diagnostic value at all in the differential diagnosis between HbS/S homozygosity and HbS/beta-thalassemia compound heterozygosity. Furthermore, the “beta-thal short column kit” (BioRad) used by the authors is designed for a reliable determination of the HbA2 level on the HPLC Variant in the absence of HbS. In the presence of HbS, the glycated products of the HbS fraction will variably overlap with the HbA2 peak (Figs. 1 and 2, shown in the article) and result, therefore, in the elevated HbA2 values reported by the authors. Glycated Hb, comprising 3% to 7% of total Hb, is normally present also in fresh blood. The HbA2 values reported by the authors are increased by the variable presence o f glycated HbS and have no diagnostic significance for hemoglobinopathy analysis, except perhaps for an indication of the (frequently) coexisting alpha-thalassemia when the HbA2 is lower than 2.5%. The Variant HPLC analyses cannot differentiate between HbS/S and HbS/beta-zero-thalassemia, if done examining the proband only. First of all, one should be sure about the non-transfused status of the patients (this detail is not mentioned by the authors!). When HbS is present in combination with a mild beta+-thalassemia, a small amount of HbA could be present on HPLC and be a diagnostic indication, but no HbA will be measurable in non-transfused HbS/S