What does the Thyroid-Stimulating Hormone test measure?

Why is Thyroid-Stimulating Hormone measured?

TSH is the first-line test of thyroid function, with elevation signalling primary hypothyroidism and suppression indicating hyperthyroidism or excessive thyroid hormone replacement. In this panel TSH provides the thyroid-pituitary axis context for the concurrent oestrogen-metabolite profile, since thyroid dysfunction influences sex-hormone metabolism and menstrual regularity.

Reference ranges

Standard reference

Approximately 0.4–4.0 µIU/mL; intervals vary by assay and population, and dried blood spot TSH correlates well with serum but requires method-specific validation.

Functional medicine optimal

Many endocrinologists and functional practitioners favour TSH values between 0.5 and 2.5 µIU/mL as optimal for well-being, particularly in early pregnancy and subclinical hypothyroidism, though treatment thresholds remain debated.

Units

µIU/mL, mIU/L, μIU/mL

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