The contribution of the haematocrit to thrombocytopenic bleeding in experimental animals


Dr Morris A. Blajchman, Department of Pathology, Room 2N31, McMaster University Medical Centre, 1200 Main Street West, Hamilton, Ontario L8N 3Z5, Canada.


Summary Clinical studies in anaemic uraemic patients have shown that increasing the haematocrit with either red blood cell (RBC) transfusions or erythropoietin corrects the prolonged bleeding time (BT) often seen in such 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 both normal and thrombocytopenic rabbits. In non-thrombocytopenic animals the microvascular BT varied inversely with the haematocrit (r=-0.799); animals with haematocrit levels above 35% having significantly shorter BTs than animals with haematocrit values lower than 35% (P < 0.001). To assess the role of the haematocrit on the BT in thrombocytopenic animals, thrombocytopenia was induced by a combination of γ-irradiation and heterologous platelet antiserum. Such experiments showed that anaemic rabbits had significantly longer BTs than non-anaemic animals with a similar degree of thrombocytopenia (P=0.0001). These data thus provide evidence that anaemia contributes significantly to the prolonged BT in both thrombocytopenic and non-thrombocytopenic rabbits, and that RBC transfusions are capable of shortening the BT in thrombocytopenic anaemic animals. While results obtained from animal models cannot necessarily be extrapolated to the clinical situation, 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.