The combined use of monoclonal antibody-based enzyme-linked immunosorbent assays (ELISA) for factor VIII antigen (VIII:Ag) and von Willebrand factor antigen (vWF:Ag) for the detection of carriers of haemophilia A

Enzyme-linked immunosorbent assays (ELISA) for factor VIII antigen (VIII:Ag) and von Willebrand factor antigen (vWF:Ag) have been developed, each employing monoclonal antibodies. In the majority of severe haemophilic plasmas tested, VIII:Ag was undetectable by ELISA and also by immunoradiometric assay (IRMA) using haemophilic VIII:C antibodies. In haemophilic plasmas with mild/moderate deficiency of coagulant factor VIII (VIII:C), there was no significant difference between the two immunoassays although there was a general trend for ELISA VIII:Ag results to be higher. Assay of von Willebrand's disease (vWd) plasmas with the ELISA for vWF:Ag demonstrated reduced levels of this antigen in type I vWd, normal levels in type IIA, and a severe reduction of vWF:Ag in type III vWd. The discrimination of obligate carriers of haemophilia from normal was determined using ratios of factor VIII/vWF. Factor VIII antigen/von Willebrand factor antigen measured by IRMA and Laurell immunoelectrophoresis respectively, gave a superior discriminant to that of VIII:C/vWF:Ag (Laurell), but optimal discrimination was obtained with the combination of ELISAs for VIII:Ag and vWF:Ag.