Thyroid-stimulating hormone: first-line thyroid screening test from the pituitary.
What it is
TSH in mIU/L (mU/L) drives the thyroid to release T4/T3. Pregnancy has different targets: tell the lab if pregnant or planning.
TSH from the pituitary is the most sensitive routine marker of primary thyroid dysfunction. Assays report mIU/L. Free T4 (and sometimes FT3) complete the picture.
Why it matters
TSH is interpreted with free T4 (and sometimes free T3) and your symptoms. High or low TSH can have several causes; only a qualified clinician can diagnose thyroid conditions. Mention biotin supplements if you take them, as they can interfere with some assays.
This guide is educational only and cannot diagnose you. Discuss results, especially anything outside your laboratory’s reference interval, or that does not match how you feel, with a GP or other appropriately qualified clinician.
How it affects the body
The hypothalamic–pituitary–thyroid axis adjusts TSH to keep thyroid hormone supply matched to demand. Thyroid hormones set metabolic rate in virtually every tissue.
Endurance athletes with unexplained fatigue, cold intolerance, or menstrual change may have thyroid tests, but overtraining and low energy availability mimic some symptoms. Do not adjust thyroxine doses from a consumer panel without your prescriber.
Fatigue in sport has many causes; thyroid tests help when symptoms fit, but low energy availability mimics hypothyroid complaints. Never adjust thyroxine from a consumer panel without your prescriber.
For fertility planning when you want AMH with key reproductive and thyroid markers in one private panel. AMH does not predict natural conception chances.
