The effect of platelets on the in vitro response to prothrombin complex concentrates in F.VIII inhibitor plasma.

Incubation of prothrombin complex concentrates, both non-activated and activated, in plasma enhances coagulation. The effect is reduced with time and is augmented when platelets are present. Such concentrates correct the coagulation abnormality in vitro in haemophilic plasmas with factor VIII inhibitors and the correction is greater in platelet rich than platelet poor plasma. Platelets appear to protect incubated concentrates from inhibitors present in plasma. Platelets may play a role in mediating the in vivo clot-promoting activity of some components of these concentrates. This effect may contribute to unwanted thrombosis or, conversely, may facilitate the sometimes-observed haemostatic effect of concentrates in patients with inhibitors of factor VIII.