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Thyroid-Stimulating Hormone (TSH) Test

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 What is the thyroid-stimulating hormone (TSH) test?
 Why is this test done?
 How do I prepare for this test?
 How is it done?
 What does the test result mean?
 What if my test result is not normal?

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What is the thyroid-stimulating hormone (TSH) test?

This blood test measures how well your thyroid gland is working. This gland, which is located at the lower front of the neck, may be normal, underactive, or overactive. The test measures your body's response to the thyroid hormone level in your blood.

Your body’s pituitary gland controls the activity of your thyroid gland by producing thyroid-stimulating hormone (TSH).

Why is this test done?

The TSH test is used to:

  • Check for thyroid disease
  • Monitor thyroid hormone medicine levels
  • Look for thyroid disease in newborns
  • Diagnose female infertility problems

The TSH test is one of several thyroid tests used to check for thyroid disease. The thyroid gland makes hormones that go into your bloodstream and control how fast your body’s cells do their work. The thyroid gland is critical for maintaining body temperature and controlling heart rate, appetite, digestive tract function, and your energy level.

How do I prepare for this test?

  • You may need to avoid taking certain medicines before the test because they might affect the test result. Make sure your healthcare provider knows about any medicines, herbs, or supplements that you are taking. Ask your healthcare provider before you stop taking any of your regular medicines.
  • Talk to your healthcare provider if you have any questions.

How is it done?

Having this test will take just a few minutes. A small amount of blood is taken from a vein in your arm with a needle. The blood is collected in tubes and sent to a lab.

Ask your healthcare provider when and how you will get the result of your test.

What does the test result mean?

Normal values are usually shown next to your results in the lab report. Normal values for blood thyroid level vary from lab to lab, depending on the testing method.

A higher than normal TSH level means there is not enough thyroid hormone in your blood. This condition is called hypothyroidism. You may have hypothyroidism because:

  • Your thyroid gland is damaged.
  • Your thyroid gland is not working normally.
  • Your thyroid gland is infected or inflamed.
  • You had an overactive thyroid gland that was removed or destroyed and you are not taking enough replacement thyroid hormone.
  • Your pituitary gland (the gland in your brain that produces TSH) is making too much TSH, and that makes your thyroid gland make too much thyroid hormone. This is rare.

A lower than normal TSH level means there is too much thyroid hormone in your blood. This condition is called hyperthyroidism. You may have hyperthyroidism because:

  • You had an overactive thyroid gland that was removed or destroyed and you are taking too much replacement thyroid hormone.
  • Your thyroid gland is infected or inflamed.
  • Your thyroid gland has grown too large.
  • Your thyroid has a tumor that is producing extra thyroid hormone.

What if my test result is not normal?

Test results are only one part of a larger picture that takes into account your medical history and current health. Sometimes a test needs to be repeated to check the first result. Talk to your healthcare provider about your result and ask questions, such as:

  • If you need more tests
  • What kind of treatment you may need
  • When you need to be tested again
  • What lifestyle, diet, or other changes you might need to make
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References

National Endocrine and Metabolic Diseases Information Service (NEMDIS). Hyperthyroidism. US Dept of Health and Human Services, National Institutes of Health, National Institute of Diabetes and Digestive and Kidney Diseases. 8/2012. Accessed 4/2014 from http://www.endocrine.niddk.nih.gov/pubs/Hyperthyroidism/#causes.

LabTestsOnline. TSH.11/28/2012. Accessed 1/28/2013 from http://labtestsonline.org/understanding/analytes/tsh/tab/test.

WebMD. Thyroid-stimulating Hormone. June 11, 2008. Accessed 10/28/2010 from http://www.webmd.com/a-to-z-guides/thyroid-stimulating-hormone-tsh.

Lab Tests Online; TSH; accessed on 6-9-09 at http://labtestsonline.org/understanding/analytes/tsh/test.html.


Related Topics

Thyroid-Stimulating Hormone (TSH) Test

Hyperthyroidism (High Thyroid Level)

Hypothyroidism (Low Thyroid Level)

Thyroid Hormone Blood Test


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Last Modified: 2014-04-29

Last Reviewed: 2014-04-29

Website Updated: October 2014

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This content is reviewed periodically and is subject to change as new health information becomes available. The information is intended to inform and educate and is not a replacement for medical evaluation, advice, diagnosis or treatment by a healthcare professional.


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