FREE PROTEIN-S DEFICIENCY IS A RISK FACTOR FOR VENOUS THROMBOSIS

A recent study suggests that protein S deficiency is not a risk factor for venous thrombosis. Since this unexpected finding would have impor tant clinical implications if confirmed, we performed a case-control s tudy with the aim to determine the prevalence of protein S deficiency in patients with thrombosis and in healthy individuals taken from the general population and the relative risk of thrombosis in protein S-de ficient patients. Free protein S concentration was measured in 327 con secutive patients with at least one venous thrombotic episode and in 3 17 age-and sex-matched control individuals. Different normal reference ranges were obtained and adopted for men and women. Protein S deficie ncy was found in 3.1% (95% CI: 1.5-5.2) of patients and in 1.3% of con trols (95% CI: 0.3-2.8). Ten patients and 4 control subjects had prote in S deficiency, which determined a relative risk of thrombosis (sex-a nd age-adjusted odds ratio) of 2.4 (95% CI: 0.8-7.9). When men and wom en were analyzed separately, the risk was 5.0 (95% CI: 0.6-43.6) and 1 .6 (95% CI: 0.4-6.7) respectively. PS-deficient men had more thromboti c episodes than women and later in life. Multivariate analysis establi shed that sex was an independent determinant of the number of episodes , as was age, while PS deficiency was not. However sex and PS deficien cy status were both determinants of age at first thrombotic episode.