Clinical Interpretation of Thyroid Tests: Considerations for Reference Intervals

As thyroid disease is common and can present with nonspecific symptoms, thyroid function tests are one of the most widely requested laboratory investigations. The serum thyrotropic (TSH) concentration is an effective rule-out test for primary thyroid disease when used in the context of appropriate reference intervals. The dependence of the TSH reference intervals on iodine status, ethnicity, age, and pregnancy is well described and the use of relevant reference intervals is widely recommended. However, the provision of appropriate reference intervals can be challenging due to the complex and costly, clinical, ethical, operational, and financial requirements associated with establishing prospective reference cohorts as well as the methodological differences that still plague thyroid function tests.