Prevalence of antithrombin deficiency in healthy blood donors: a cross-sectional study.

The prevalence of antithrombin (AT) deficiency in the general population has been variously estimated to be between 0.05 and 5 per 1,000 in the population; 2,491 blood donors were screened in an attempt to clarify this issue using plasma samples taken from the blood donor units. From this initial population, 122 individuals were identified as having plasma AT levels lower than 2 standard deviations below the normal mean. Twenty-two samples had evidence that thrombin had been generated during blood collection and the remaining cohort of 100 blood donors were asked to return but only 59 complied. The data obtained from these 59 were compared with that from 51 age- and sex-matched control blood donors. Both groups of subjects were assessed for previous evidence, or family history, of thrombotic events, as well as exposure to risk factors associated with the development of deep vein thrombosis (DVT). All had venous blood samples taken from which the supernatant plasma was immediately removed and quick frozen for later assaying. Only 6 of the 59 subjects with initial low AT levels had repeat AT-Xa levels below 0.80 units/ml (normal range 0.94 +/- 0.14). Upon repeating the AT-Xa determinations on new samples from these six individuals, only three were found again to be low. One was found to have a type 3 AT deficiency (an Arg47Cys substitution). The other two with a low AT level had mean functional AT-Xa levels of 0.61 and 0.71 units/ml, respectively, with correspondingly low AT:Ag levels consistent with a type 1 AT deficiency. Two of these three subjects has been in high risk situations without evidence of having developed DVT and none had evidence of venous reflux on Doppler venography. In addition, none had personal or family histories of previous thrombotic events. These present data indicate that the prevalence of AT deficiency in our blood donor population is 2 per 1,000 (95% confidence intervals: 0.7-6/1,000).