PREVALENCE OF ANTITHYROID PEROXIDASE ANTIBODIES IN AUTOIMMUNE AND NONAUTOIMMUNE THYROID-DISORDERS IN A RELATIVELY LOW-IODINE ENVIRONMENT

We evaluated the prevalence of antithyroid peroxidase antibodies (anti -TPO Ab) in 402 patients with thyroid disease and 30 healthy controls by a commercial radioimmunoassay (RIA) and compared the results with t he passive hemagglutination (HA) method. The patients in the study had autoimmune thyroid disorders (AITD) such as Graves' disease and Hashi moto's disease or had nonautoimmune thyroid diseases (NAITD) such as t hyroid cancer, congenital goiter, endemic goiter, and nodular goiter. Subjects were recruited from a population with a mild iodine deficienc y (Sao Paulo, Brazil). The effect of specific therapy (for either thyr otoxicosis or chronic thyroiditis) on the circulating anti-TPO levels was also investigated, Positive anti-TPO Ab was detected in 89.9% of t he patients with AITD as compared with a prevalence of positive tests of only 4.8% in patients with NAITD. Positive microsomal antibody (M A b) was found in 68.4% of the patients with AITD and in 6.4% of the pat ients with NAITD. A positive and significant correlation was obtained between M Ab and anti-TPO Ab. A positive anti-TPO test with negative a nti-M was found in 14.1% of the patients with AITD but in only 4.3% of the patients with NAITD and normal controls, These results suggest th at anti-TPO Ab by RIA is more sensitive and specific than M Ab by HA. In patients with AITD, anti-TPO Ab levels usually decreased after trea tment, suggesting that this parameter could be used in the follow-up o f these thyroid disorders.