Red cell indices and discriminant functions in the detection of beta-thalassaemia trait in a population with high prevalence of iron deficiency anaemia.

Red cell indices and discriminant functions were studied in 463 heterozygous beta-thalassaemics (337 without iron deficiency, 126 with iron deficiency) and 195 patients of iron deficiency anaemia (IDA) to ascertain their utility in the detection of betathalassaemia trait (BTT). Majority of traits in both groups had an elevated RBC count (> or = 5.0 x 10(12)/L). The counts were significantly higher than of patients with IDA, only 4.6% of whom had this degree of erythrocytosis. Mean Hb concentration was significantly higher in traits as compared to iron deficient subjects (p < 0.0001). Mean MCV and MCH were significantly (p < 0.0001) lower in traits more so in those with ID as compared to patients of IDA. MCV < 80 fl and MCH < 27 pg were found to be sensitive markers in the detection of traits even in the presence of ID. Of the four discriminant functions studied MCSQ was found to be most sensitive in detection of BTT and it identified 97.9% traits. DF of England and Fraser was most specific for BTT being < 8.4 in only 6.2% patients with IDA. Detection of erythrocytosis especially in the presence of mild anaemia and calculation of discriminant functions derived from red cell indices were found to play an important role in screening for BTT even in the presence of ID and helped identify those patients who required further laboratory evaluation.