Assessment of the Value of Factor VIII Procoagulant and Antigen Ratio in the Diagnosis of Carriers of Haemophilia*

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Abstract
The detection rate of carriers of hemophilia was evaluated using the ratio of factor VIII procoagulant activity (VIIIc) to factor VIII antigen (VIIIag). In normals the correlation coefficient of VIIIc to VIIIag was 0.82. In 15 obligatory carriers of hemophilia whose VIIIc and VIIIag levels were studied there was no correlation between VIIIc and VIIIag and the ratio of VIIIc to VIIIag was below the lowest normal value in 12 (80%). In all 5 obligatory carriers whose VIIIc levels were estimated in the referring institution and VIIIag levels the ratio was below the lowest normal value. In 17 sisters of hemophiliacs studied or referred for estimation of VIIIag only, an abnormal ratio was found in 7. Of 25 mothers of hemophilic children without a family history of hemophilia 16 had an abnormal ratio. This incidence of hemophilia carriers is close to that expected on theoretical grounds but the interpretation of the results is complicated by the small numbers of patients. In 2 normal individuals, one of who was on a contraceptive pill, there were no fluctuations of the ratio of VIIIc to VIIIag during the menstrual cycle. In 1 obligatory carrier with a normal ratio there was also no fluctuation. A measurement of the ratio of VIIIc to VIIIag is a valuable adjuvant in genetic counselling in hemophilia.