TSH (Thyroid-Stimulating Hormone) Test
Reviewed
Also called: Thyrotropin, Thyroid-stimulating hormone, Thyrotropic hormone
A TSH test is a blood test that measures this hormone. A TSH level that is too high or too low may be a sign of a thyroid problem.
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
You may need to stop taking certain medicines before this test, so tell your provider about everything you take. But don't stop taking any medicines unless your provider tells you to.
A health care professional will take a blood sample from a vein in your arm, using a small needle. This usually takes less than five minutes.
There is very little risk to having a blood test. You may have slight pain or bruising at the spot where the needle was put in, but most symptoms go away quickly.
Understanding results
Your TSH test results can tell you if your thyroid is making too much or too little hormones. But the test can't explain why your TSH levels may be too high or too low.
What does high or low TSH mean?
TSH too high or too low: A TSH level that is too high or too low may be a sign of a thyroid problem. Limitation: But the test can't explain why your TSH levels may be too high or too low. Next step: If your test results aren't normal, your provider will probably order other thyroid blood tests to find out what's causing your thyroid problem.- High or low TSH with a healthy thyroid: Your TSH level may be high or low even when your thyroid gland is healthy. Limitation: Some serious illnesses (that are not related to your thyroid) may cause a lower TSH level for a short time. The TSH level may be higher in people over age 80, even though they don't have any thyroid problems. Next step: If you have a history of thyroid disease, be sure to talk with your provider if you are pregnant or are thinking of becoming pregnant.
- 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
If your test results aren't normal, your provider will probably order other thyroid blood tests to find out what's causing your thyroid problem.
- 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
Source: U.S. National Library of Medicine (MedlinePlus). Practices and reference ranges may differ in your country.
U.S. National Library of Medicine: TSH (Thyroid-Stimulating Hormone) Test