Heterogeneity of haemophilia A: a study with three different antisera

One human and one rabbit antibody against VIII:C--in a fluid-phase, inhibitor neutralization assay (INA)--and one human antibody--in a solid-phase, immunoradiometric assay (IRMA)--were used to investigate a group of 59 patients with severe, moderate and mild haemophilia A. Patients were classified as haemophilia A+ when the VIII:C/VIIIAG ratio was less than 0.4 while the absolute VIII:C antigen (VIIICAG) value exceeded 0.25 u/ml. Three haemophiliacs (from two pedigrees) were classified as A+ in all three assay systems. 50% of the patients were classified as haemophilia A+ on the basis of at least one assay. The other 50%, including 66% of the patients with severe haemophilia, were shown to be A- by all three assay systems. Combining the data obtained with the three different antibodies four different categories could be distinguished, in addition to the classification based on severity.