Summary
Assays for platelet coagulant activities concerned with the initiation and progress
of intrinsic coagulation were done pair-wise in two groups of 16 haemophiliacs without
detectable factor VIII. The patients in the ‘severe’ group had experienced 7.9-22.8
(mean 13.7) spontaneous haemorrhages per 100 days during an average of 431 days of
observation, whereas those in the ‘mild’ group had bled 0-5.5 (mean 3.2) times per
100 days during an average of 282 days of observation. Contact product forming activity,
collagen-induced coagulant activity and intrinsic factor-Xa forming activity were
decreased in the severely-affected group and increased in the mildly affected group,
whereas there was no great difference in platelet factor 3 activity between the two
groups. Variations of platelet coagulant activities concerned with the initiation
and early stages of intrinsic coagulation may influence clinical severity in haemophilia.
