Monthly hemostatic factor variability in women and men

Background— Hormonal status influences hemostatic factors including fibrinogen, factor VII and plasminogen activator inhibitor (PAI-1), and concentrations differ among men, premenopausal and postmenopausal women. This study examines how phases of the menstrual cycle influence variability of fibrinogen, factor VII and PAI-1. Design— We studied 103 subjects (39 premenopausal women, 18 postmenopausal women, and 46 men) during three, randomized, 8-week energy and nutrient-controlled experimental diets in the DELTA (Dietary Effects on Lipids and Thrombotic Activity) Study. Fasting blood samples were collected weekly during the last four weeks of each diet period and hemostatic factors were quantified. Two linear mixed-effects models were used for fibrinogen, factor VII and PAI-1: one to estimate and compare group-specific components of variance, the other to estimate additional fixed effects representing cyclical functions of day of menstrual cycle in premenopausal women. Results— Systematic cyclical variation with day of menstrual cycle was observed for fibrinogen (p<0.0001), factor VII (p=0.0012), and PAI-1 (p=0.0024) in premenopausal women. However, the amplitude of cycling was small relative to the total magnitude of intra-individual variability. In addition, the intra-individual variance and corresponding coefficient of variation observed in premenopausal women did not differ from postmenopausal women and men. Conclusions— The variability in hemostatic factors in premenopausal women is no greater than for postmenopausal women or men. Consequently, premenopausal women can be included in studies investigating hemostatic factor responses without controlling for stage of menstrual cycle.