Double-AntibodyRadioimmunoassayfor Factor Vill-Related Antigen

A plasma protein required for the support of ristocetininduced platelet aggregation was isolated from antihemophilic factor concentrate and radiolabeled with 1251. A double-antibody radioimmunoassay was developed, with use of specific rabbit anti-Vill related antigen serum and goat anti-rabbit globulin. The assay is sensitive, reproducible, and technically simple to perform. Values obtained in normal subjects ranged from 0.65 to 1.53 units, similar to cur normal range for VIII coagulant activity (0.67-1.43 units). However, normal or increased values of VIlI-related antigen were observed in VIII coagulant-deficient hemophiliacs. Also, concentrations of VIll-related antigen significantly exceeded coagulant concentrations in several patients with liver disease or disseminated intravascular coagulation, or both. Of a broad selection of congenital coagulation disorders examined, only patients with von Willebrand’s disease had decreased Vlll-related antigen concentrations, and these corresponded to the lowered concentration of ristocetin cofactor in the patients. In three transfused patients, VOl-related antigen values correlated with the concentration of the cofactor. Our results suggest that the radioimmunoassay of VIll-related antigen is a simple and valuable adjunct in the study of patients with clotting abnormalities.