Thyroid antibodies in blood donors: prevalence and clinical significance.

In sera from 1643 randomly selected blood donors examined in 1979 thyroglobulin antibodies (TGA) were found in 3.4% and thyroid microsomal antibodies (TMA) in 7.0%. TMA, but not TGA, showed significant sex and age relationships. Eight-two donors with TMA titres greater than or equal to 1600 and/or TGA titres greater than or equal to 128 were available for a follow-up study in 1982. In 69 of these with TMA there was a significantly increased incidence of pathological thyroid function-test values (T4, T3 and TSH) as compared to age- and sexmatched donors without thyroid antibodies. In this group 9 individuals had overt and three latent hypothyroidism, two individuals were found with symptomless autoimmune thyroiditis and one with a non-toxic nodular goitre. Only 2 of these had been diagnosed before 1982, and none recognized before 1979. In addition, the group contained 9 individuals who had been treated because of hyperthyroidism, all except one before 1979. The likelihood of detecting a previously unrecognized hypothyroidism increased with increasing TMA titre. In contrast, the 24 donors with TGA did not show an increased frequency of pathological thyroid function-test-values in 1982.