TSH (Thyroid-stimulating hormone)

Thyroid-stimulating hormone (TSH) is released by anterior pituitary thyrotrophs and regulates thyroid hormone production via negative feedback from circulating T3 and T4. In primary thyroid disease it is the most sensitive single marker of thyroid status: higher values typically indicate hypothyroidism, while suppressed values suggest hyperthyroidism or exogenous hormone excess. In central (pituitary or hypothalamic) hypothyroidism, TSH may be inappropriately normal or low alongside low fT4, so combined interpretation with free T4 is required. Reference ranges shift slightly upward with age, and subclinical dysfunction is common in older adults.