Effect of age, sex, and diurnal variation on the human fibrinolystic system.

Fibrinolytic activity, as shown by the dilute blood clot lysis time, tends to show a diurnal variation, but is relatively unaffected by age and sex. Mean plasma anti-urokinase activity is consistently and significantly greater in females in the post-menstrual week than in age-matched males, but is relatively unaffected by daily variation and age. This sex difference in the activity of plasma, which is inhibitory to fibrinolysis, is of a degree which makes this measurement important in studies of the fibrinolytic system in healthy persons and disease states.