Pitfalls in the use of thyrotropin concentration as a first-line thyroid-function test.

Measurement of thyrotropin concentration alone as a first-line thyroid-function test fails to indicate hypopituitarism in a number of patients. Using a combination of thyrotropin and thyroxine assays, we analysed 56,000 tests for a population of 471,000 over 12 months. 15 patients with clinically unsuspected hypopituitarism were detected, indicating that the occurrence of hypopituitarism might be underestimated.