What is the purpose of measuring T3 autoantibodies and T4 autoantibodies?
In dogs, antibodies which cross-react with T4 and/or T3 are markers for lymphocytic thyroiditis. These antibodies are generated against T4 and T3 containing epitopes on the thyroglobulin molecule, i.e., they are subsets of TgAA. Positive values indicate thyroid gland pathology, and also tell us about the validity of the thyroid hormone results. T3AA and T4AA are present in around 35% and 14% of hypothyroid dogs respectively. In the Endocrine Diagnostic Section at Michigan State University, T3 antibodies cause a false decrease in TT3 and a false increase in FT3 results. T4 antibodies falsely increase TT4 and may increase FT4 results in the standard thyroid profiles. In a hypothyroid dog with T4AA, T4 may be falsely elevated into the normal range and the true diagnosis masked. To obtain an accurate measure of T4 status in a T4AA positive animal, submit a sample for free T4 by equilibrium dialysis (FT4d) which is not affected by antibody. FT4d is included in Premium Thyroid Profiles. Alth
