Assessment of the value of factor VIII procoagulant and antigen ratio in the diagnosis of carriers of haemophilia.

The detection rate of carriers of haemophilia was evaluated using the ratio of factor VIII procoagulant activity (VIIIc) to factor VIII antigen (VIIIag). In normals the corelation coefficient of VIIIc to VIIIag was 0.82. In 15 obligatory carriers of haemophilia whose VIIIc and VIIIag levels were studied in the authors' labotatory 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 five obligatory carriers whose VIIIc levels were estimated in the referring institution and VIIIag levels in the authors' laborary the ratio was below the lowest normal value. In 17 sisters of haemophiliacs studied here or referred for estimation of VIIIag only, an abnormal ratio was found in seven. Of 25 mothers of haemophilic children without a family history of haemophilia carriers is close to that expected on theoretical grounds but the interpretation of the results is complicated by the small numbers of patients all of whose studies were performed entirely in the authors' laboratory. In two 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 one obligatory carrier with a normal ratio there was also no fluctuation. It is concluded here that a measurement of the ratio of VIIIc to VIIIag is a valuable adjuvant in genetic counselling in haemophilia.