The role of ultrasensitive thyroid-stimulating hormone measurement in the initial evaluation of thyroid function

New ultrasensitive assays of thyroid-stimulating hormone (TSH) have been introduced recently and recommended as better first line tests of thyroid function. The previous biochemical thyroid function tests are reviewed, with details of their usefulness and limitations. The limitations of the new ultrasensitive TSH assays are also reviewed. Although there are advantages in using TSH compared to other tests, the cost versus benefits ratio have yet to be assessed. Clinicians should be aware of the limitations in any biochemical test of thyroid function and treatment should not be based on laboratory investigation alone.