Factor VII activation and oral contraceptives

The relation between oral contraceptive (OC) use and changes in factor VII activation using standard factor VII clotting test and enzyme-linked immunosorbent assay (ELISA) for the quantification of antigen factor VII (factor YIIag) in view of the increased risk of thromboembolism in OC users was studied. 30 healthy women using OC and 30 women matched for age and smoking status were recruited from a health check-up center in Paris. The combined OC contained 50 mcg of ethinyl estradiol with any progestogen. Controls had not taken any hormonal therapy for the 2 previous months. The mean duration of OC use was 50 months with a range of 6-204 months. Fasting venous blood (9 volumes) was collected during the menstrual cycle into siliconized vacutainer tubes containing 3.2% trisodium citrate (1 volume). Factor VIIc was assayed using a human factor VII-deficient plasma. Factor VIIag was measured by ELISA using a commercial kit (Diagnostic Stago France). The activity of factor VII was assessed by calculating the ratio of factor VIIc to factor VIIag. Serum cholesterol and triglyceride concentrations were determined by enzymatic methods using automated procedure and reagents from Boehringer Mannheim. There was a significant difference between the 2 groups only in serum triglyceride concentrations. There was a positive correlation between factor VIIc and factor VIIag in both controls and OC users (r = 0.71 and 0.87 respectively; p < 0.0001). Both factor VIIc and factor VIIag levels were positively associated with serum triglyceride concentrations (correlation coefficients ranged from 0.26 (p < 0.10) to 0.46 (p < 0.05) with the 2 groups). Mean levels of factor VIIc and factor VIIag were significantly higher in OC users than in controls (about 17% and 21% respectively). The ratio of factor VIIc and factor VIIag was not significantly higher in OC users than in controls. The raised factor VII coagulant activity in OC users failed to provide evidence of an enhanced activation of factor VII relative to OCs.