RESUMO
BACKGROUND: Protein C (PC) with its cofactor free protein S (FPS) are important anticoagulants. Any defect in the PC system is a risk factor for venous thrombosis. AIMS: To assess the effect of intensity of smoking, and the dose-response for the number of cigarettes smoked on PC and FPS plasma levels. METHODS: A comparative study was designed and carried out on a convenient sample of 50 healthy non-smokers and 150 non-symptomatic Jordanian male smokers. PC and FPS levels were measured using an automated system (Stago Analyzer, USA). RESULTS: The plasma level of PC among smokers was 7.2% lower than that among non-smokers (p = 0.02). Moreover, smokers had 15.6% lower circulating FPS than non-smokers (p = 0.001). Furthermore, data showed significant negative correlations between both PC and FPS levels and the intensity of smoking (r = -0.21%, r = -0.23%, respectively; p = 0.01) and the period of smoking (r = -0.15%, r = -0.23%, respectively; p = 0.01, 0.12, respectively). CONCLUSIONS: The PC and FPS plasma levels were significantly lower in smokers than non-smokers. Both PC and FPS levels correlated inversely with the period and intensity of smoking, and FPS was more sensitive to smoking than PC.