A comparative study of carrier detection in haemophilia A by linear discriminant function

Blood samples collected from 37 definite carriers, 31 normal women and 64 possible carriers were examined for factor VIII-related activities. Five variables: factor VIII coagulant activity (VIII:C) (X1), factor VIII-related antigen (VIIIR:Ag) (X2), ristocetin co-factor (VIIIR:RC) (X3), ratio of VIIIR:Ag to VIII:C (A/C) (X4) and ratio of VIII:RC to VIII:C (R/C) (X5), and 28 combinations of one to five variables were used to derive 28 linear discriminant functions. The calculation of discriminant function coefficient, individual discriminant score and cut-off point, and the identification of normals or carriers were processed by the computer package of a biomedical computer program used at University of California at Los Angeles. A comparison of 28 linear discriminant functions for carrier detection in haemophilia A has indicated that the best and simplest is y = 0.11668X1 (VIII:C)--0.06042X2 (VIIIR:Ag), (cut-off point y = 2.03742). It identified 94.6% of carriers without a single misclassification in the normal group, and the overall identification rate was 97.1%. Of 29 daughters of definite carriers who had no haemophilic sons, 13, or 44.8%, could be identified as carriers. It was found that VIII:RC was not as good as VIIIR:Ag for carrier detection; however, it may be concluded from this study that VIIIR:RC can be used as a supplement, if not a substitute, for VIII:Ag in the carrier detection of haemophilia A.