Protein C, antithrombin III and plasminogen: effect of age, sex and blood group.

We conducted a cross-sectional study of antithrombin III (ATIII), protein C (PC) and plasminogen (Plg) concentrations in a population of healthy plasma donors in the Trent Region. The distribution of values for protein C was log normal whereas for ATIII and Plg the distributions were positively skewed and differed significantly from normal and log normal. Males had higher antithrombin III concentrations (mean 1.10 iu/ml, range 0.72-1.65) than females (mean 1.07 iu/ml, range 0.75-1.69) (P = 0.001) and levels increased with age in women. Younger women aged 25-34 had significantly lower plasma concentrations of ATIII compared to males of similar age. For protein C, concentrations were higher in males (mean 1.07 u/ml, range 0.37-2.11) than in females (mean 1.01 u/ml, range 0.59-1.61) (P < 0.001) and levels increased with age in both sexes P < 0.001). In women, a novel difference in protein C concentration between ABO blood groups was noted. There was no significant difference in plasminogen concentration between males and females, and in women plasminogen decreased with age (r = -0.205, P < 0.001). We conclude that these variations in ATIII and protein C with age and sex are important considerations in the determination of reference ranges for these proteins.