Measurement of Thyroid Stimulating Hormone: Utility and Pitfalls

Physiological production of thyroid hormone requires an intact hypothalamic-pituitary-thyroid (HPT) axis and involves thyroid-stimulating hormone (TSH, or thyrotropin) released from the anterior pituitary gland. TSH stimulates thyroid follicular cells to synthesize, store and release the thyroid hormones thyroxine (T4) and triiodothyronine (T3) [1]. Chemical laboratory testing of thyroid function involves, first, assessment of levels of the hormones and, then, correlation of those levels with the clinical state of the patient. TSH is used to screen for thyroid disease and is the most reliable test to diagnose common forms of both hypothyroidism and hyperthyroidism [1]. Current guidelines of the American Thyroid Association recommend screening adults, beginning at age 35 and every 5 years thereafter. This strategy appears to be especially cost-effective for women and the elderly [2]. Persistently low TSH levels have been associated with higher cardiovascular mortality, and hypothyroidism during pregnancy has been associated with both increased fetal loss and impaired intellectual ability of offspring [1,2].