A TSH (thyroid-stimulating hormone) test is a blood test that measures the amount of TSH in your blood. TSH is produced by the pituitary gland in your brain, and it prompts the thyroid gland to make and release thyroid hormones into your blood. The test is used to find out how well your thyroid is working and can tell if you have hyperthyroidism (too much thyroid hormone) or hypothyroidism (too little thyroid hormone) in your blood. A TSH test cant show what is causing a thyroid problem, but it can detect a thyroid disorder before you have any symptoms.

To perform the test, a healthcare provider will take a sample of blood from a vein in your arm and send the sample to a laboratory for testing. You usually don’t need to do anything special to prepare for a TSH blood test, but if your healthcare provider has ordered other blood tests, you may need to fast (not eat or drink) for several hours before the test.

Normal TSH levels vary slightly among different laboratories, and some labs use different measurements or test different samples. If you are being treated for a thyroid disorder, your TSH level will likely be kept between 0.5 and 4.0 µU/mL, except when a pituitary disorder is the cause of the thyroid problem, in which case a low TSH may be expected.

There is very little risk to having a blood test, and you may have slight pain or bruising at the spot where the needle was put in, but most symptoms go away quickly. If you have questions about your TSH test results, ask your healthcare provider.