Normalized activated protein C ratio itself not associated with increased risk of venous thromboembolism

Recently, discussions focused on the question whether acquired activated (A PC) resistance is a clue to the observed association between venous thrombo embolism (VTE) risk and oral contraceptive (OC) use, especially with the so -celled third-generation OC. The objective of our study was to check the validity of acquired APC resist ance regarding VTE risk in a case-control study. Sixty-seven women with con firmed VTE diagnosis (n = 67) were consecutively ascertained in primary hea lth care settings, interviewed and blood samples taken (at the earliest 6 m onths after VTE). Cases were age-matched to 290 population controls. Acquir ed APC resistance was measured as normalized APC ratio (APCR(N)). The effec t of APC on tissue factor initiated thrombin generation was measured in pla sma using a,; macroglobulin attached thrombin activity as an endpoint. High er risk (odds) ratio with 95% CI) of VTE for carriers of heterozygote Facto r V Leiden mutation was confirmed [OR = 2.72 (CI:1.51-4.92)]. However there is no association between VTE and the level of APCR(N) OR 0.65 (CI:0.35-1. 22). WE conclude that acquired APC resistance, measured with a tissue factor ini tiated test, is unlikely to have a direct association to the clinical outco me of venous thromboembolism. (C) 1998 Elsevier Science Inc. All rights res erved.