[Amplitude of the distribution of erythrocyte size in the differential diagnosis of microcytic anemia].

A prospective study was carried out in 83 patients with microcytic anemia. 43 had iron deficiency anemia, 28 had heterozygous beta thalassemia not associated with iron deficiency (beta-THNID) and 12 had both conditions. The behavior of red blood cell volume distribution width (RDW) was evaluated in all patients. RDW was higher in patients with iron deficiency (20.62 +/- 4.64) and beta-THNID (15.76 +/- 1.41) than in controls (13.29 +/- 0.92) (p less than 0.0001 for both comparisons). There also were statistically significant differences (p less than 0.0001) between both patient groups. In patients with both heterozygous beta thalassemia and iron deficiency (beta-THID), RDW reached similar values to those from patients with only iron deficiency anemia. A significant negative correlation was also found between the transferrin saturation index and RDW (r = -0.614, p less than 0.02). In 34 patients controlled during iron replacement therapy a significant increase of RDW was found after one month of treatment, while hemoglobin concentration and mean corpuscular volume became normal. When 18 was taken as cutoff value for RDW, its positive predictive value was very high in iron deficiency (95%), while it was only 59% in beta-THNID. England's index may help to differentiate between isolated iron deficiency anemia and beta-THID: in patients with RDW higher than 18, the positive predictive value of England's index was 89% for iron deficiency and 57% for beta-THID.(ABSTRACT TRUNCATED AT 250 WORDS)