Thyroid function studies. Test strategies and interpretation of results.

Biochemical tests for detection of thyroid dysfunction in persons without underlying systemic illness are highly effective. In fact, one or more of the following tests are sufficiently diagnostic to allow initiation of appropriate treatment: thyroxine (T4), free T4 index (FT4-I), thyrotropin (TSH), and triiodothyronine (T3). Only rarely is it necessary to measure free T4 concentration or perform a thyrotropin-releasing hormone (TRH) stimulation test. Patients with underlying illnesses, on the other hand, frequently exhibit unexpectedly abnormal test results depsite euthyroidism. Thus, if clinically feasible, thyroid function testing should be postponed in such patients.