Thyroid antibodies in healthy blood donors.

The frequency of thyroid antibodies was investigated in 1314 healthy blood donors. Twenty-three of 870 males (2.6%) were positive for thyroglobulin antibody (TA), 34 (3.9%) for thyroid microsomal antibody (MA) and 19 (2.2%) for both TA and MA. Thirty-four of 484 females (6.2%) were positive for TA, 46 (9.5%) for MA and 29 (6.0%) for both TA and MA. Eighty-six of 1314 blood donors were positive for TA and/or MA. There was no difference in liver function tests between AAT and controls. In females, the incidence of thyroid antibodies tended to increase with age. However, the subjects aged under 19 showed another peak of incidence of thyroid antibodies. The values of total T4, T3 and free T4 were not different between 86 subjects with positive thyroid antibodies (asymptomatic autoimmune thyroiditis, AAT) and 86 sex- and age-matched controls without thyroid antibodies, whereas serum TSH of AAT was significantly higher than that of controls. Nine of 86 (10.5%) subjects with AAT had apparently increased basal TSH level.