IMMUNORADIOMETRIC ASSAY OF INHIBITORS OF ANTIHAEMOPHILIC FACTOR A

Abstract

An immunoradiometric assay (IRMA) for determination of antibodies against factor VIIIC in hemophilia A was developed. The assay was based on competitive binding of radiolabeled anti-VIII:C and antibodies in the test material to immobilized VIII:C. Hemophiliacs (15) with known inhibitors were investigated with the new method and with a conventional neutralization test. In 3 cases the inhibitors were detected only with the IRMA and in the other 12 there was good agreement between the inhibitor levels found with both methods. It was also possible to demonstrate the antibodies in 3 nonhemophilic patients with acquired inhibitors. The IRMA, which can detect the antibodies down to a concentration of 0.02 inhibitor units/ml, is more sensitive than conventional neutralization tests and is of practical importance in the investigation of patients with low inhibitor titers.