RESISTANCE TO ACTIVATED PROTEIN-C IN UNSELECTED PATIENTS WITH ARTERIAL AND VENOUS THROMBOSIS

Four hundred and ninety-three consecutive patients referred for arteri al or venous thrombosis were screened for congenital and acquired abno rmalities of blood coagulation predisposing to thrombosis, and were co mpared to 341 age- and sex-matched controls, The aim of the study was to determine the prevalence and clinical characteristics of resistance to activated protein C (APC), a defect shown to have different preval ences in different ethnic groups and to be associated with an increase d risk of thrombosis, Seventy-three (15%) patients had both APC resist ance and the 1691 G to A factor V gene mutation, compared to 6/341 (2% ) controls, Seven patients had antithrombin deficiency (1.4%), 11 had protein C deficiency (2.2%), and 4 had protein S deficiency (0.8%), Th e relative risk of thrombosis in APC-resistant patients was 9.4. Resis tance to APC was associated mainly with venous thrombosis, the most fr equent being deep-vein thrombosis of the lower limbs. Fifty-eight perc ent of APC-resistant patients had an associated risk factor at the fir st thrombotic event: pregnancy and oral contraceptive intake were asso ciated with the first thrombotic episode in 35% and 30% of women, resp ectively, APC resistance is the most frequent defect of blood coagulat ion in the general population and in the unselected thrombotic populat ion studied by us. (C) 1997 Wiley-Liss, Inc.