Thyroid antibodies: diagnostic implications

Abstract

Thyroid antibody measurements are becoming an essential part of the array of diagnostic tests useful in some specific clinical circumstances. Antibodies to thyroid hormones also can cause interference with thyroid function tests. There are at least three autoantigens 1. thyroglobulin; 2. microsomal 3. the TSH receptor. Antithyroglobulin and antithyroidal microsomal Ab are measured in patients suspected of having thyroiditis. Antithyroidal microsomal Ab are more specific than antithyroglobulin Ab for Hashimoto’s and occur in almost all patients with this disorder. Recently, it has been reported antithyroblobulin and thyroid microsomal Ab may influence prognosis of Grave’s patients treated with antithyroid drugs. TSH receptor antibodies are characteristic of Graves’ disease, but also occur in a few patients with Hashimoto’s thyroiditis. At least two types of antibodies are recognized. TRAb assays have been used to predict relapse from drug therapy, to predict thyroid function in the newborn, and in difficult diagnostic cases. Autoantibodies to thyroxine, triiodothyronine, or both are commonly are found in patients with Hashimoto’s thyroiditis or Graves’ disease and also occur in patients without thyroid disease. The reported prevalence of thyroid antibodies Ab is from less than 1% to about 40% probably depending on the methods used to determine Ab presence and the population of patients studied. In the presence of thyroid Ab, results for T4 and T3 measurements can be falsely low or high depending on the immunoassay used. Thyroid antibody measurements are becoming an essential part of the array of diagnostic tests useful in some specific clinical circumstances. Antibodies to thyroid hormones also can cause interference with thyroid function tests. There are at least three autoantigens 1. thyroglobulin; 2. microsomal 3. the TSH receptor. Antithyroglobulin and antithyroidal microsomal Ab are measured in patients suspected of having thyroiditis. Antithyroidal microsomal Ab are more specific than antithyroglobulin Ab for Hashimoto’s and occur in almost all patients with this disorder. Recently, it has been reported antithyroblobulin and thyroid microsomal Ab may influence prognosis of Grave’s patients treated with antithyroid drugs. TSH receptor antibodies are characteristic of Graves’ disease, but also occur in a few patients with Hashimoto’s thyroiditis. At least two types of antibodies are recognized. TRAb assays have been used to predict relapse from drug therapy, to predict thyroid function in the newborn, and in difficult diagnostic cases. Autoantibodies to thyroxine, triiodothyronine, or both are commonly are found in patients with Hashimoto’s thyroiditis or Graves’ disease and also occur in patients without thyroid disease. The reported prevalence of thyroid antibodies Ab is from less than 1% to about 40% probably depending on the methods used to determine Ab presence and the population of patients studied. In the presence of thyroid Ab, results for T4 and T3 measurements can be falsely low or high depending on the immunoassay used.