A Case of Hypothyroidism due to Hashimoto Disease that Presented Elevations of Free T₃ and Free T₄ by Thyroid Hormone Autoantibodies

Abstract

When we commonly evaluate the thyroid function, we measure TSH, free T₃ and free T₄. However, there are some cases that are difficult to diagnose because of the existence of thyroid hormone autoantibodies. We experienced a case of a 14-year-old girl with diffuse struma whose TSH, free T₃ and free T₄ were elevated by detected with Amerlex M free T₃ and free T₄ kits, although she did not have any symptoms. As the free T₄ level was low by the equilibrium dialysis method, we diagnosed this case as hypothyroidism due to chronic thyroiditis. Because we found thyroid hormone antibodies in her serum, we thought that this case presented pseudoelevations of free T₃ and free T₄ by the analogue method.