INFLUENCE OF DEMOGRAPHIC-FACTORS ON ANTITHROMBIN-III ACTIVITY IN A HEALTHY POPULATION

Antithrombin III (AT III) activity has been measured in 9669 healthy b lood donors (5525 male and 4144 female). The distribution of AT III is approximately 'normal' with mean 105.6 iu/dl and standard deviation 1 1.2; however. definite age and sex related variations are evident. Pre -menopausal females have lower mean AT III compared to their male cont emporaries who have remarkably stable mean AT III until 4 5 years, aft er which there is a gradual decline. In contrast, post-menopausal fema les have higher mean AT III than both males of the same age and younge r pre-menopausal females. Concurrent hormone replacement therapy inhib its this rise. The use of hormonal preparations is associated with a 4 iu/dl reduction of mean AT III in younger females but not in those ov er 30 years. Smoking may result in a mild increase in AT III of doubtf ul clinical significance. On-going genetic and family studies are expe cted to predict a prevalence rate of congenital AT III deficiency in e xcess of the previously reported figure of 0.02%. The authors consider these observed variations as minor and recommend the use of a single reference range for AT Ill activity, but that particular care be taken when interpreting results in pill-taking females and the elderly.