RESISTANCE TO ACTIVATED PROTEIN-C IN AN UNSELECTED POPULATION OF PATIENTS WITH PULMONARY-EMBOLISM

Background Resistance to activated protein C (APC) is the most frequen t cause of inherited thrombophilia. This phenomenon has been reported in 10-50% of selected patients with venous thromboembolism, a variatio n that might result from different degrees of selection in different r eports. Methods We measured the APC sensitivity ratio in 494 frozen bl ood samples from unselected consecutive outpatients suspected of pulmo nary embolism and referred over a 30-month period to the emergency war d of the University Hospital of Geneva, the only public primary-tertia ry care hospital in the region of Geneva (400 000 inhabitants). Findin gs Prevalence of resistance to APC was 55% (95% CI 2.4-10.5%) (8/146) in patients with confirmed pulmonary embolism and 4.0% (2.2-6.7%) (14/ 348) in patients in whom the diagnosis could be ruled out (p=0.66), gi ving an odds ratio of 1.36 (0.56-3.32). Interpretation The very differ ent risks of venous thromboembolism in the presence of resistance to A PC that have been reported in trials published so far are probably due to variable recruitment conditions. The lower prevalence observed in our totally unselected population of patients with pulmonary embolism may be more representative of the real risk with which clinicians will be confronted. Therefore, more data are needed from various populatio ns of patients with venous thromboembolism to help decide which patien ts will benefit from screening for resistance to APC.