THE CONTRIBUTION OF THE HEMATOCRIT TO THROMBOCYTOPENIC BLEEDING IN EXPERIMENTAL-ANIMALS

Clinical studies in anaemic uraemic patients have shown that increasin g the haematocrit with either red blood cell (RBC) transfusions or ery thropoietin corrects the prolonged bleeding time (BT) often seen in su ch individuals. In this present study we evaluated experimentally the effect of the haematocrit on the BT using a microvascular BT technique in New Zealand White rabbits. The correlation between haematocrit and BT was studied in bath normal and thrombocytopenic rabbits. In non-th rombocytopenic animals the microvascular BT varied inversely with the haematocrit (r= -0.799); animals with haematocrit levels above 35% hav ing significantly shorter BTs than animals with haematocrit values low er than 35% (P<0.001). To assess the role of the haematocrit on the BT in thrombocytopenic animals, thrombocytopenia was induced by a combin ation of gamma-irradiation and heterologous platelet antiserum. Such e xperiments showed that anaemic rabbits had significantly longer BTs th an non-anaemic animals with a similar degree of thrombocytopenia (P=0. 0001). These data thus provide evidence that anaemia contributes signi ficantly to the prolonged BT in both thrombocytopenic and non-thromboc ytopenic rabbits, and that RBC transfusions are capable of shortening the BT in thrombocytopenic anaemic animals. While results obtained fro m animal models cannot necessarily be extrapolated to the clinical sit uation, the fact that haematocrit influences the BT must be taken into account in the assessment of anaemic patients, particularly those who may have an associated haemostatic disorder.