Carrier detection in classical hemophilia.

Rabbit antibody to purified human factor VIII was prepared and absorbed until it formed only one precipitin line against normal and hemophilic plasmas and no line against severe von Willebrand's disease plasma. The plasma protein which combines with this rabbit antibody to factor VIII is referred to as factor VIII antigen. The ratio of percent factor VIII activity (by coagulation assay) to percent factor VIII antigen was used for carrier detection. Thirty-seven normal women, 33 obligate carriers, 12 probable carriers, and 39 possible carriers, were studied by this technique. Using the ratio of 0.84 as the division between normals and carriers, 31 of the 33 carriers (91%) were classified carriers. Twenty of the 39 possible carriers were classified as carriers (51%) and ten of the 12 probable carriers were positively identified. The results of discriminate analysis of all three variables (VIII activity, VIII antigen, and the ratio of VIII activity to VIII antigen indicated that the discrimination power of the ratio alone could not be improved by introducing the other variables on this set of data. These findings confirm the usefulness of the VIII activity to VIII antigen ratio in the detection of carriers of classical hemophilia.