Effect of oral contraceptives on factor VIII clotting activity and factor VIII related antigen in normal women.

Abstract

and the Haemophilia Centre, Royal Free Hospital, London2 SYNOPSIS The factor VIII clotting activity (VIII) and factor VIII related antigen (VIIIRAg) were determined repeatedly in 24 pairs of age-matched normal women, one of each pair being on oral contraceptives. No significant differences in either parameter or in the VIIIC/VIIIRAg ratio were found between the two groups, although the mean factor VIII clotting activity and VIIIc/VIIIRAg ratios for women on oral contraceptives were very slightly higher than for those not on oral contraceptives.The demonstration by Zimmerman et al (1971) that the ratio VIIIc/VIIIRAg is decreased in carriers of haemophilia has led to a more reliable method of identifying the carrier state than is possible when only factor VIII clotting activity is measured. Since many suspected carriers of haemophilia take oral contraceptives, it is important to determine whether the use of these drugs results in a change of the VI11/VIIIRAg ratio. Egeberg and Owren (1963) found that they led to an increase in the level of factor VIII clotting activity in normal women while Schiffman and Rapaport (1966) found an increase in factor VIII clotting activity levels in suspected carriers of haemophilia who were taking oral contraceptives. Their effect on factor VIII related antigen has not been previously reported. We present here the results of factor VIII clotting activity and factor VIII related antigen determinations on two groups of normal women, one on oral contraceptives and the other off them.