Effect of Oral Contraceptives on Factor VIII Clotting Activity and Factor VIII Related Antigen in Known Haemophilia Carriers

The factor VIII clotting activity (VIII:C) and factor VIII related antigen (VIIIR:AG) were determined on 3 occasions in 14 known haemophilia carriers, each paired with an age-matched control, both groups being on oral contraceptives (O.C.), and 18 known carriers each paired with an age-matched control, neither group on O.C. The VIII:C/VIIIR:AG ratio was less than 0.7 in 14 out of 14 carriers on O.C. and greater than 0.7 in 13 out of 14 controls on O.C. 16 out of 18 carriers not on O.C. had a ratio less than 0.7 while 16 out of 18 controls not on O.C. had a ratio greater than 0.7. Statistical analysis showed that there was no significant difference in the accuracy of carrier detection in this group of known carriers, whether or not they were on oral contraceptive pills.