Interaction Between Oral Contraceptive Use and Coagulation Factor Levels in Deep Vein Thrombosis

Background: Since not all women using oral contraceptives (OC) develop deep vein thrombosis (DVT), the presence of additional risk factors in women with DVT and OC use is likely. High levels of coagulation factor activities are established risk factors of DVT. There are, however, limited data on the combined effect of OC use and high levels of procoagulant coagulation factors, a shortened aPTT or markers of inflammation like erythrocyte sedimentation rate (ESR) or CRP.

Materials and Methods: 246 women with a first DVT (123 associated with OC use) and 246 normal women matched for age and date of birth were evaluated. Cut-off values for continuous variables were the 90% percentile determined in normal women. OC use influences the levels of many coagulation factors. Using the mean effect of OC use on coagulation factor levels (measured in the control subjects), we estimated the coagulation factor levels in patients prior to the index date, i.e. the time of the thrombosis.

Results: Use of OC was associated with an increase in risk of 3.0. This risk increased due to interaction with factor I (FI) (Odds Ratio (OR) 14.2, p=0.0001), FVIII (OR 5.1, p=0.0001), FIX (OR 5.5, p=0.0001), FXI (OR 12.0, p=0.0001), vWF:Ag (OR 7.7, p=0.0001) and aPTT (OR 20.2, p=0.004). In contrast, no significant increase in risk was found when OC use was associated with high levels of ESR or CRP.

Conclusion: The results of this study indicate that the joint effects of OC use and high coagulation factor levels increase the risk of DVT. This risk increase appears to be of clinical relevance particularly in individuals with shortened aPTT values or high levels of fibrinogen.