Routine screening for coagulation inhibitors prior to prescribing the pill: prevalence data from a large cohort of German pill starters.

A total of 2674 women were recruited to participate in a multicenter oral contraceptive (OC) study on hemostasis. At baseline, protein S activity less than 60% of normal values was found in two volunteers (0.75 per 1000) and the antithrombin III activity was less than 60% of normal values in three volunteers (1.1 per 1000). All measurements were confirmed by a second assessment. In contrast, of the 28 women presenting with protein C levels less than 60% of normal values, only six were confirmed (2.3 per 1000). Of these, one was also protein S-deficient. Seven women could not be studied twice and 15 were false-low according to their normal control values. These data suggest that routine screening of the hemostatic system may reveal findings suggestive of inhibitor deficiencies in as many as 3.75 per 1000 of apparently healthy candidates for OCs. However, our data also demonstrate that unselected screening is compromised by a considerable rate of false-positive results and cannot generally be recommended. However, screening of coagulation inhibitors is feasible in women with a family history of thromboembolic disease.