A simple model for estimating the hemolytic rate in patients with sickle cell anemia

The pathophysiologic processes of hemolysis in sickle cell anemia were formulated by a simple mathematical model that assumed a unimodal bone marrow erythrocyte population and a finite probability of random destruction of red blood cells (RBCs) in the circulation. Recognizing that the hemolytic rate of marrow RBCs is likely to be distributed normally around a mean hemolytic rate, we simplified the model by using the mean hemolytic rate as representative of the entire marrow RBC population. The model thus constructed allows an easy estimation of the mean steady-state hemolytic rate simply by measurement of reticulocyte counts and hematocrit levels. When the model was applied to data from 43 patients with sickle cell anemia, the estimated mean hemolytic rates based on the model correlated significantly with the published hemolytic rates obtained by diisopropylphosphofluoridate-RBC survival studies of the peripheral blood, but were generally greater than the published rates. This discrepancy was postulated to be the result of an enrichment of RBCs with smaller hemolytic rate in the circulation. The results of computer simulation studies were consistent with this hypothesis and suggest that the variation in the hemolytic rate for marrow RBCs is on the order of 10%. This simplified model may serve as a close approximation of this pathophysiologic system. The estimates of the steady-state hemolytic rate provided by the model should be clinically useful, especially when repeated estimations are required. The method of calculation is illustrated.