Protein C deficiency in a controlled series of unselected outpatients: an infrequent but clear risk factor for venous thrombosis (Leiden Thrombophilia Study) - Koster, T; Rosendaal, FR; Briët, E; Van der Meer, FJM; Colly, LP; Trienekens, PH; Poort, SR; Reitsma, PH; Vandenbroucke, JP (Blood, 1995)