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

Summary. 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.