Red cell distribution width as a measure of severity of iron deficiency in iron deficiency anaemia

Of the various red cell parameters used for distinguishing iron deficiency anaemia (IDA) from beta-thalassaemia trait BTT, red cell distribution width (RDW), which is an objective measure of the degree of anisocytosis, was examined by us for its discriminating value. RDW was measured in 55 patients of IDA and 56 patients of BTT at presentation with the help of an automated haematology analyser. The mean RDWs in IDA and BTT patients were 18.2 +/- 3.8 and 15.1 +/- 1.2 respectively (P < 0.001). In IDA, RDW showed an inverse relationship with the haemoglobin level (r = -0.543; P < 0.001), while no such correlation was observed in BTT patients. An inverse relation was also observed in IDA between RDW and transferrin saturation (TS). Patients with high RDW had low TS and vice versa. The latter finding, although statistically not significant, suggested that the degree of elevation of RDW in IDA could reflect the severity of iron deficiency. Our study revealed that red cell count, which was significantly higher in BTT patients (P < 0.001), the RDW, and the discriminant function (DF) calculated from these two parameters could be useful in distinguishing IDA from BTT. A RDW above 17.1 strongly suggests the presence of IDA. For RDW below 17.1 the DF can be applied for further discrimination. RDW has the advantage of being obtained directly from the analyser, while DF is a calculated value.