Elevated Plasma Fibrinogen and Increased Fibrin Turnover among Healthy Women who both Smoke and Use Low-dose Oral Contraceptives

Abstract

Among users of low-dose oral contraceptives (OC), cardiovascular diseases occur mainly in smokers. The mechanisms by which OC and smoking increase the risk for arterial thrombotic risk have not been adequately explained. Epidemiological evidence suggests that changes in blood coagulation and fibrinolysis may play an important role as determinants of thrombotic events. Therefore, we have investigated the associations of OC and smoking with haemostatic variables among 194 premenopausal healthy women. Fourty women were current users of low-dose OC and 62 women were smokers. After adjustment for age and body mass index, mean values of factor XIIa, factor VII activity and antigen, fibrinogen, D-dimer, global fibrinolytic capacity were significantly higher in OC users than in non-users. Mean levels of PAI activity and t-PA antigen were significantly lower in OC users than in non-users. Smokers had significantly higher mean values of fibrinogen than non-smokers. Two-way analysis of variance showed that the differences in mean levels of fibrinogen and D-dimer between OC users and non users were restricted to smokers. The positive and significant interactions between OC use and smoking in their effects on haemostatic variables were consistent with respect to age and type of OC. These preliminary data suggest that elevated plasma levels of fibrinogen and intravascular fibrin deposition may play a role in the pathogenesis of arterial thrombotic disease among women who are both low-dose OC users and smokers.