Carrier Detection in Haemophilia A by Immunological Measurement of Factor VIII Related Antigen (VIIIRAg) and Factor VIII Clotting Antigen (VIIICAg)

Abstract

Obligate [human] carriers of mild and severe hemophilia A and 26 normal females were bled on 3 occasions, and their plasmas assayed for procoagulant factor VIII (VIIIC), factor VIII related antigen (VIIIRAg) and factor VIII clotting antigen (VIIICAg). A comparison of the ratios VIIIC/VIIIRAg and VIIICAg/VIIIRAg indicated that, although the 2 ratios gave the same proportional misclassification of carriers as normals (4 of 23), the latter ratio showed greater discriminatory power when an unequal variances predictive method was used to calculate likelihood ratios (for carrier status). This greater power was due to a greater reproducibility between visits for the VIIICAg/VIIIRAg ratio. Discrimination was considerably better when the median of the 3 median values for each variable was analyzed, compared to the median value obtained at the 1st visit. There was also no statistical difference between VIIICAg/VIIIRAg (or VIIIC/VIIIRAg) ratios obtained from carriers of severe compared to mild hemophilia.