PREVALENCE OF ANTITHROMBIN DEFICIENCY IN THE HEALTHY POPULATION

In a cohort of 9669 blood donors we have identified 16 cases of congen ital AT deficiency (1 in 600) by way of family studies and AT gene ana lysis. Two donors had type I AT deficiency (prevalence 0.21 per 1000; 95% CI = 0.03/1000 to 0.75/1000), their families displaying a symptoma tic phenotype. 14 donors had a type II deficiency (prevalence 1.45 per 1000; 95% CI = 0.79/1000 to 2.43/ 1000): one recurring and three uniq ue mutations. None of these type II deficiencies appeared to confer a high thrombotic risk despite many of the affected individuals having e xperienced potentially prothrombotic challenges. The high frequency of these relatively asymptomatic variants may reflect a selection bias i n the study population. However, their existence should not only add t o our understanding of structure-function relationships of AT but may also influence our management of asymptomatic deficient individuals id entified in epidemiological or pre-surgical screening programmes.