Abstract
Factor VIII related antigen has been measured and epitope distribution has been explored by testing the degree of parallelism between standard and test plasma dose response curves using an enzyme immunoassay. Normal plasma, plasma fractions, and plasma from patients with haemophilia and von Willebrand's disease have been tested. All showed parallelism except for plasma from patients with the variant type IIA von Willebrand's disease, of which 10 had parallel and five had non-parallel dose response curves when compared with that of normal plasma. In one family plasma from seven members showed parallelism but from four others did not. An unrelated patient was tested on three occasions, and although the samples were parallel to each other, no sample was parallel to the standard. No correlation was found between parallelism as shown by the enzyme immunoassay and differences in factor VIII related antigen multimeric pattern, including triplet configuration, seen in the type IIA patients.