Summary

Thrombin generation was investigated in platelet-rich plasma(PRP) from 11 healthy controls, 17 patients with severe haemophiliaA and 7 patients with severe haemophilia B. Mean endog-enousthrombin potential (ETP) in arbitrary fluorescence units(FU) was 226.9 ± 44.6, 186.4 ± 22.5, 154.2 ± 41.3 in controls,haemophilia A and B, respectively, all at a platelet count of200 10 9 /l (p = 0.004 for controls vs. haemophilia A, p = 0.003for controls vs. haemophilia B, no significant difference betweenhaemophilia A and B). The contribution of FVIII to thrombingeneration in haemophilia A was 1.31 ± 0.16 FU/% of FVIII:Cactivity, while for FIX in haemophilia B this was 0.80 ± 0.21FU/% of FIX activity. There was an almost linear relationshipbetween increasing platelet count and thrombin generation upto a mean platelet count of 100 10⁹/l. Further increase inplatelet count has only a marginal influence on thrombingeneration. Platelets increase ETP in haemophilia A by 0.184 ±0.022 FU/10⁹ platelets/l and in haemophilia B by 0.319 ±0.085 FU/10⁹ platelets/l, and this was significantly differentbetween the two groups (p = 0.0002). This influence of plateletsdiminishes with increasing concentration of either FVIII orFIX. In conclusion, there is a difference in thrombin generationbetween haemophilia A and B, and this may be attributed tothe role of platelets in the assembly of the tenase complex ontheir surface.