The incidence of occult thyroid disease associated with thyroid antibodies identified on routine autoantibody screening.

The presence of thyroid microsomal and/or thyroglobulin antibodies has been recorded over a 2 year period of 15 000 consecutive autoimmune profile request. Where there had been no initial clinical suspicion of thyroid diseases, 332 requests showed positive thyroid antibodies, and of these 63 (19%) had abnormal in vitro thyroid function tests (TFT). No differences were observed between the abnormal and normal groups with respect to the presence of different autoantibodies or to the age and sex distributions. Of these subjects with clinically unsuspected hypothyroidism but with abnormal TFTs, 29% were commenced on thyroxine therapy and experienced a symptomatic improvement, 25% remain well on no therapy and 9% continue on no treatment but with symptoms possibly attributable to hypothyroidism. 3% became clinically hypothyroid during a follow-up period of 2 years. 5% died of unrelated causes and there was inadequate follow-up information on the remainder. This study provides further confirmation that when thyroid antibodies, and in particular thyroid microsomal antibody, are found unexpectedly, a significant proportion of patients will have biochemical evidence of hypothyroidism and may benefit from appropriate treatment.