Thyroid Stimulating Hormone (TSH)

Thyroid-stimulating hormone (TSH) is secreted by the anterior pituitary gland under the control of thyrotropin-releasing hormone (TRH), a tripeptide produced by the hypothalamus. TSH stimulates the synthesis and secretion of thyroxine (T4) and triiodothyronine (T3) by the thyroid gland. The circulating free fractions of T4 and T3 regulate TSH secretion through a negative feedback mechanism acting at the pituitary and, to a lesser extent, the hypothalamus. Circulating free T4 and T3 regulate TSH secretion via negative feedback at the pituitary and, to a lesser extent, the hypothalamus.

Measurement of serum TSH is central to the assessment of thyroid function. In overt hypothyroidism, reduced total or free T4 concentrations are typically accompanied by an elevated TSH level, confirming primary thyroid failure. Conversely, suppressed or undetectable TSH concentrations are characteristic of hyperthyroidism, in which circulating T4 and T3 levels are increased.

Highly sensitive TSH assays, commonly referred to as “third-generation” assays, have functional sensitivities in the range of 0.01–0.02 mIU/L. These assays allow reliable discrimination between the markedly suppressed TSH concentrations observed in thyrotoxicosis and the low but detectable concentrations seen in subclinical hyperthyroidism.

Store tightly capped at 15–30°C for ≤18 hours; 2–8°C if testing is delayed beyond 18 hours; freeze at ≤ –20°C if testing is delayed beyond 7 days. Frozen specimens may be stored for up to 90 days.

Lipemic or hemolyzed specimens.

Enhanced Chemiluminescence.

0.34–5.60 μIU/ml

• Evered DC. Diseases of the thyroid gland. Clin Endocrinol Metab. 1974;3:425–450.
• Evered DC, et al. Grades of hypothyroidism. Br Med J. 1973;1:657–662.
• Caldwell G, et al. A new strategy for thyroid function testing. 1985;1:1117–1119.
• Spencer CA. Thyroid profiling for the 1990s: free T4 estimate or sensitive TSH measurement. J Clin Immunol. 1989;12:82–89.

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