Report of the Working Party on Factor VIII Related Antigens

Detection of haemophilia carriers: multivariate analysis compared with discriminant analysis using up to five factor VIII variates

Multivariate analysis is potentially superior to the linear discriminant analysis which is commonly used to identify carriers of haemophilia. Our aim was to compare these two statistical methods, and to find which factor VIII variates most effectively partitioned carrier and normal subjects. In this study we assayed one- and two-stage factor VIII coagulant activity, factor VIII related antigen by electroimmunoassay and by fluoroimmunoassay, and ristocetin co-factor in 50 normal females and 50 carriers of haemophilia. From the results we calculated multivariate ellipses which circumscribed the normal and the carrier populations, and we displayed these on the monitor of a microcomputer. These ellipses separated the two populations better than linear discriminants calculated on the same data. Multivariate analysis correctly identified 94% of the carriers whereas discriminant analysis correctly identified only 84%. Discriminant analysis gave poorer results because the statistical assumption of equal variance was breached, whereas the assumption of multivariate normality was upheld. Of the five factor VIII variates, two-stage factor VIII coagulant activity and factor VIII related antigen by electroimmunoassay correctly identified the most subjects. Ristocetin co-factor did not improve the diagnostic ability, either when in lieu of or when added to factor VIII related antigen.

Fast migrating protein, immunochemically related to human factor VIII, studied by crossed immunoelectrophoresis in agarose

A fast migrating protein (FMP) was detected by agarose radio-crossed immunoelectrophoresis, in addition to factor VIII antigen (VIII:RAg), using antiserum to human factor VIII (FVIII). FMP had partial immunochemical identity with FVIII, migrated as an alpha-protein, and was distinct from alpha-2 macroglobulin, fibronectin or IgM. FMP was precipitated by concanavalin A and was separable from the bulk of VIII:RAg by ammonium sulphate fractionation. A significant amount of FMP was seen in normal serum (n = 12), plasma from patients with: (a) disseminated intravascular coagulation (n = 12) and (b) severe haemophilia A (n = 6). Trace amounts of FMP were observed in plasma from normal donors (n = 12), but neither VIII:ARg nor FMP was detectable in the plasma or serum from patients with severe von Willebrand's disease (n = 3). Freshly prepared cryoprecipitate contained trace amounts of FMP, similar to normal plasma, but increased levels were observed in antihaemophilic factor concentrates prepared for patient use. Significant levels of FMP were also seen in cryoprecipitate after storage at 4 degrees C for 7 d and this generation of FMP was diminished by the addition of protease inhibitors. The presence of significant levels of FMP in situations where proteolytic enzymes may be activated and inhibition of its generation by protease inhibitors, suggest that this protein is produced by proteolytic action of enzyme(s) on the FVIII molecule.