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A thyroid-stimulating hormone (TSH) test measures the amount of TSH in the blood. TSH is produced by the pituitary gland, which is located at the base of your brain. It’s responsible for regulating the amount of hormones released by the thyroid.
The thyroid is small, butterfly-shaped gland located in the front of the neck. It’s an important gland that creates three primary hormones:
The thyroid controls numerous different bodily functions, including metabolism and growth, through the release of these three hormones.
Your thyroid will produce more hormones if your pituitary gland produces more TSH. In this way, the two glands work together to make sure the right amount of thyroid hormones are produced. However, when this system is disrupted, your thyroid can produce either too many or too few hormones.
A TSH test is often performed to determine the underlying cause of abnormal thyroid hormone levels. It’s also used to screen for an underactive or overactive thyroid gland. By measuring the level of TSH in the blood, your doctor can determine how well the thyroid is working.
Your doctor may order a TSH test if you’re experiencing symptoms of a thyroid disorder. Thyroid diseases can be categorized as either hypothyroidism or hyperthyroidism.
Hypothyroidism is a condition in which the thyroid produces too few hormones, causing metabolism to slow down. The symptoms of hypothyroidism include fatigue, weakness, and difficulty concentrating. The following are some of the most common causes of hypothyroidism:
Hyperthyroidism is a condition in which the thyroid produces too many hormones, causing the metabolism to speed up. Symptoms of hyperthyroidism include increased appetite, anxiety, and difficulty sleeping. The following are some of the most common causes of hyperthyroidism:
The TSH test doesn’t require any special preparation. However, it’s important to tell your doctor if you’re taking medications that might interfere with the accuracy of the TSH measurement. Some medications that could interfere with a TSH test are:
You may need to avoid using these drugs before the test. However, don’t stop taking your medications unless your doctor tells you to do so.
A TSH test involves taking a sample of blood. The blood is typically drawn from a vein that’s inside the inner elbow.
A healthcare provider will perform the following procedure:
The entire procedure should only take a few minutes to complete. The blood sample will be sent to a lab for analysis. Once your doctor receives the test results, they’ll schedule an appointment with you to discuss the results and explain what they may mean.
The normal range of TSH levels is 0.4 to 4.0 milli-international units per liter. If you’re already being treated for a thyroid disorder, the normal range is 0.5 to 3.0 milli-international units per liter.
A value above the normal range usually indicates that the thyroid is underactive. This indicates hypothyroidism. When the thyroid isn’t producing enough hormones, the pituitary gland releases more TSH to try to stimulate it.
A value below the normal range means that the thyroid is overactive. This indicates hyperthyroidism. When the thyroid is producing too many hormones, the pituitary gland releases less TSH.
Depending on the results, your doctor may want to perform additional tests to confirm the diagnosis.
Written by: Lauren Reed-Guy
Medically reviewed on: Jan 20, 2016: Steve Kim, MD
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