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Factor‐VIII Antigen and Platelet Retention in a Glass Bead Column

Summary. Platelet retention by the method of Bowie et al (1969a, b) was investigated and its diagnostic value in von Willebrand's disease (VWD) confirmed. Platelet retention was not affected by variations of heparin concentration, by inverting the blood or by a delay of up to 2 hr in performing the tests. Cryoprecipitate prepared from normal and from haemophilic plasma with normal factor‐VIII antigen levels corrected the abnormal platelet retention in VWD in vitro, whereas cryoprecipitate prepared from VWD plasma with reduced factor‐VIII antigen concentration was ineffective. This suggested, in agreement with our previous findings (Bouma et al, 1972), that factor‐VHI‐related antigen is responsible for the in vitro correction of the abnormal platelet retention in VWD. Circulating inhibitors of factor VIII activity had no effect on the platelet retention of normal blood, suggesting that the site on the factor‐VIII molecule which potentiates platelet retention is not affected by blocking the molecular site which is responsible for the factor‐VIII activity. A normal factor‐VIII antigen level was found in four patients with VWD. Cryoprecipitate prepared from plasma of these patients corrected the abnormal platelet retention of patients with VWD who had reduced factor‐VIII antigen concentration. These results suggest that VWD is heterogeneous.