Erythrocyte indices as screening tests for the differentiation of microcytic anemias

Algorithms for the differential diagnosis of anemias are commonly based on suspected incidences and simple laboratory parameters. Especially microcytic anemias are diagnosed using algorithms created in Mediterranean or Northern American regions. In a West German region we observe relatively high diagnostic uncertainty regarding common forms of anemias. As a hypothesis, this may be a result of inadequate algorithms not designed for regions with high incidences of anemias of chronic disease and low incidences of thalassemias. To further elucidate diagnostic problems we here report the frequencies of anemias in university hospital outpatients. Based on these data, the diagnostic values of different erythrocyte indices and of red cell distribution width in the differential diagnosis of anemias were calculated. 4525 patient files were reviewed retrospectively. 872 patients presented with anemia, 107 of which were hereditary forms and 765 of other forms. In hereditary anemias the frequency of thalassaemias (50 patients) and corpuscular hemolytic anemias (49 patients) was the same. Nearly half of the other anemias were covered by anemias of chronic disease and true iron deficiency anemias. Several indices intended to separate thalassemias from other microcytic anemias were tested for relevance. Sensitivity was between 0.75 and 0.85. Specificity was between 0.78 and 0.95. Red cell distribution width was not significantly different between thalassemias and iron deficiency. Only a red cell distribution width above 17.0 resulted in a specificity for iron deficiency of 0.91. Red cell distribution width is considered to be an unreliable screening test in a population with a low incidence of thalassemias. The high incidence of anemias of chronic disease in the region investigated should lead to more complex diagnostic procedures than offered by blood count values alone.