What does the Thyroid Stimulating Hormone (Thyrotropin) test measure?

Why is Thyroid Stimulating Hormone (Thyrotropin) measured?

TSH is the primary anchor of the LabCorp Thyroid Panel — the most sensitive first-line marker for primary hypothyroidism, subclinical hypothyroidism, overt hyperthyroidism, and subclinical hyperthyroidism. An elevated TSH indicates pituitary detection of insufficient thyroid hormone; a suppressed TSH indicates suppression from excess thyroid hormone, exogenous thyroid replacement, or autonomous thyroid secretion. Interpreted alongside Free T4 and Total T4 within the panel, TSH establishes the axis of thyroid dysfunction and determines whether the Free T4 findings represent a primary thyroid gland disorder, adequate replacement, or over-treatment. The TSH:Free T4 relationship is the primary diagnostic axis of any thyroid panel.

Reference ranges

Standard reference

0.450–4.500 mIU/L # REVIEWER FLAG: Confirm LabCorp reference range for TSH on this specific panel code — LabCorp uses a third-generation TSH assay (functional sensitivity ≤0.02 mIU/L) with an established adult reference range of 0.450–4.500 mIU/L on their standard platform. Confirm whether the panel applies age-stratified reference intervals and whether critical value thresholds (<0.020 mIU/L and >20.000 mIU/L) are flagged on LabCorp's report.

Functional medicine optimal

1.0–2.5 mIU/L (functional medicine and integrative endocrinology optimal — the TSH distribution in antibody-negative populations without thyroid pathology; used as the therapeutic target in functional thyroid optimisation and pregnancy planning). # REVIEWER FLAG: Not a mainstream ATA/AACE treatment threshold — reviewer to confirm appropriate framing.

Units

mIU/L, µIU/mL

Reference ranges vary by laboratory and assay platform. Interpret in context of the issuing laboratory's stated range.