Role of red cell distribution width in classifying microcytic hypochromic anaemia

Red cell distribution width (RDW) is an automated laboratory determination of red cell anisocytosis. The aim of the study was to analyse the role of RDW in differentiating iron deficiency anaemia (IDA) from thalassaemia trait. There were 500 patients who were screened for the study. Selection criteria of microcytic anaemia were Hb < 13 g/dl in males, Hb < 12 g/dl in females with mean corpuscular volume (MCV) < 80fl. These cases were subjected to complete iron profile and haemoglobin chromatography for definite diagnosis. The values of RDW were analysed in all these cases to see the utility of RDW in classifying microcytic anaemia; especially differentiating iron deficiency anaemia from thalassaemia minor cases. There were 133 out of 500 cases anaemic; 105/133 cases had microcytic anaemia, of which 53 had iron deficiency anaemia, 39 were thalassaemia traits, 6 were thalassaemia major, and 7 had other haemoglobinopathies. Thirty-six cases (67.92%) out of 53 iron deficiency anaemia had increased RDW, 32.08% (n = 17) had normal RDW; 71.79% (n = 28) of thalassaemia trait had increased RDW, 28.21% (n =11) had normal RDW. Evaluation of RDW as screening test to detect microcytic anaemia had sensitivity of 71.42% and specificity of 40%, Evaluation of RDW as a screening test for IDA had sensitivity of 67.9% and specificity 25%. It was found uniform increase in RDW in all cases of microcytosis. It is concluded that RDW adds useful but limited information in classifying microcytic anaemia.