Abstract
Elevated hemoglobin (Hb) A2 levels are seen in heterozygous β thalassemia and rarely in pernicious anemia, Hb Zurich, and Hb Tacoma but have not been reported in homozygous sickle cell anemia (HSCA) in the English literature. We measured Hb A2 by cellulose acetate Hb electrophoresis and densitometry in 34 children with HSCA. Nine of them (26%) displayed Hb A2 levels of 3.2 to 4.7% (normal values for our laboratory: 0.7 - 3.0%). Their Hb values (7.4 to 9.2 g/dl) and reticulocyte counts (468 to 700 x 109/1) did not differ from those of the other 25 patients. Eight of these nine children showed normal to high MCVs ranging from 77 to 100 fl; one had an MCV of 63 fl. Globin chain separation by carboxymethylcellulose chromatography following the method of Cleggs and Weatherall was performed in five of the nine high HB A2 children including the one with the low MCV, and all showed a normal α/β chain ratio ranging from 0.91 to 1.05. The fetal Hb in these five subjects ranged from 1.2 to 6.6% and was not different from the values of the other 29 HSCA patients. An elevated Hb A2 level may be found in a significant proportion of HSCA patients. In addition to careful analysis of the MCV, globin chain synthesis studies may be necessary to differentiate these patients from subjects with sickle-β thalassemia.
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