Antithyroidperoxidase antibodies: A study in healthy subjects and patients with autoimmune thyroid disease

The recent availability of a RIA technique to measure thyroid antiperoxidase antibodies (TPOAb) enables recognition of their clinical significance in diseases with an autoimmune basis. The aim of this study was to investigate the prevalence of TPOAb in healthy subjects and in patients with autoimmune thyroid disease and their relationship to classical antithyroid, (antimicrosomal [MicAb] and antithyroglobulin [TgAb]) antibodies. Eighty-eight subjects, distributed into three groups, were studied: 25 healthy controls; 25 patients with Graves' disease (GD) who were kept euthyroid with low doses of carbimazole and 38 patients with Hashimoto's thyroiditis being treated with thyroxine. Free thyroxine (FT4), ultrasensitive TSH, TPOAb, MicAb and TgAb were determined by RIA. Positive titres of TPOAb were detected in 12% of the control subjects and in 84% of the patients with GD and HT. The percentage of titres above 1,000 IU/mL represents 76% for GD and 63% for HD, and 0% for healthy subjects. A highly significant correlation (r = 0.52, p < 0.001) between the titres of TPOAb and MicAb was observed. On the contrary, no association between titres of TPOAb and TgAb was seen. Greater sensitivity and predictive value is demonstrated in the diagnosis of autoimmune thyroid disease (AITD) for TPOAb than for MicAb. From a practical point of view, it can be concluded that determination of TPOAb can be a substitute for the classical measurement of MicAb in the diagnosis of autoimmune thyroid disease.