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; Briet, E; van der Meer, JM; Colly, LP; Treinekens, PH; Poort, SR; Reitsma, PH; Vandenbroucke, JP (Blood, 1995)