TSH (Thyroid-Stimulating Hormone) Test
Reviewed
Also called: Thyrotropin, Thyroid-stimulating hormone, Thyrotropic hormone
A TSH test measures a pituitary hormone that helps regulate thyroid hormone production.
Specimen: Blood
Why this test may be ordered
- Checking for an underactive or overactive thyroid
- Monitoring thyroid treatment
- Investigating symptoms or another abnormal thyroid result
Preparation and collection
Follow the ordering clinician's instructions about timing, biotin-containing supplements, pregnancy, recent illness, and thyroid medicine schedules. Do not stop a medicine or supplement unless instructed.
A health professional usually takes a small blood sample from a vein. Collection normally takes only a few minutes.
Blood collection has a small risk of brief discomfort, bruising, light-headedness, or rarely infection at the needle site.
Understanding results
TSH is interpreted with the laboratory interval and often free T4, symptoms, pregnancy status, illness, medicines, and treatment history.
- High TSH: This pattern can be seen with an underactive thyroid or insufficient thyroid-hormone replacement, but it does not establish either diagnosis. Limitation: Other contexts—including illness, pregnancy, medicines, and pituitary disease—can alter TSH, so the cause requires clinical assessment. Next step: Review free thyroid hormones and clinical context; repeat testing may be needed.
- Low TSH: This pattern can be seen with an overactive thyroid or excess thyroid-hormone replacement, but it does not establish either diagnosis. Limitation: Other contexts—including illness, pregnancy, medicines, and pituitary disease—can alter TSH, and a low value may be transient. Next step: Review free T4/T3, medicines, symptoms, and follow-up timing.
- Intervals and targets differ in pregnancy, childhood, older age, pituitary disease, and during treatment.
- Biotin and some medicines can interfere with certain assays.
What to do next
Follow-up may include free T4, free T3, thyroid antibodies, repeat testing, or treatment review depending on the pattern.
- Which reference interval and units apply to my result?
- Could medicines, supplements, illness, or sample timing affect this result?
- Do I need a repeat test or another test before any conclusion is made?
Evidence source
U.S. National Library of Medicine: TSH (Thyroid-Stimulating Hormone) Test