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TSH test
Thyrotropin; Thyroid stimulating hormone; Hypothyroidism - TSH; Hyperthyroidism - TSH; Goiter - TSH
A TSH test measures the amount of thyroid stimulating hormone (TSH) in your blood. TSH is produced by the pituitary gland. It tells the thyroid gland to make and release thyroid hormones into the blood.
How the Test is Performed
A blood sample is needed. Other thyroid tests that may be done at the same time include:
Blood sample
Venipuncture is the collection of blood from a vein. It is most often done for laboratory testing.
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T3 test
(free or total)
T3 test
Triiodothyronine (T3) is a thyroid hormone. It plays an important role in the body's control of metabolism (the many processes the body does to func...
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T4 test
(free or total)
T4 test
T4 (thyroxine) is the main hormone produced by the thyroid gland. A laboratory test can be done to measure the amount of free T4 in your blood....
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How to Prepare for the Test
There is no preparation needed for this test. Ask your health care provider about any medicines you are taking that may affect the test results. DO NOT stop taking any medicines without first asking your provider.
Medicines you may need to stop for a short time include:
- Amiodarone
- Dopamine
- Lithium
- Potassium iodide
- Prednisone or other glucocorticoid medicines
How the Test will Feel
When the needle is inserted to draw blood, some people feel moderate pain. Others feel only a prick or stinging. Afterward, there may be some throbbing or a slight bruise. This soon goes away.
Why the Test is Performed
Your provider will order this test if you have symptoms or signs of an overactive or underactive thyroid gland. It is also used to monitor treatment of these conditions.
Overactive
Hyperthyroidism is a condition in which the thyroid gland makes too much thyroid hormone. The condition is often called overactive thyroid.
Underactive
Hypothyroidism is a condition in which the thyroid gland does not make enough thyroid hormone. This condition is often called underactive thyroid....
Your provider may also check your TSH level if you are planning to get pregnant.
Normal Results
Normal values range from 0.4 to 4.0 milli-international units per liter (mIU/L).
- TSH values can vary during the day. It is best to have the test early in the morning.
- Experts do not fully agree on what the upper number should be. Opinions vary from 2.5 to 4.0 mIU/L.
Normal value ranges may vary slightly among different laboratories. Some labs use different measurements or test different samples. Talk to your provider about the meaning of your specific test results.
If you are being treated for a thyroid disorder, your TSH level will likely be kept between 0.5 and 4.0 mIU/L, except when:
- A pituitary disorder is the cause of the thyroid problem. A low TSH may be expected.
- Someone has been treated for thyroid cancer. A low TSH may be best to prevent the thyroid cancer from coming back.
- A woman is pregnant. The normal range for TSH is different for women who are pregnant. Your provider may suggest that you take thyroid hormone, even if your TSH is in the normal range.
What Abnormal Results Mean
A higher-than-normal TSH level is most often due to an underactive thyroid gland ( hypothyroidism ). There are many causes of this problem.
Hypothyroidism
Hypothyroidism is a condition in which the thyroid gland does not make enough thyroid hormone. This condition is often called underactive thyroid....
A lower-than-normal level may be due to an overactive thyroid gland, which can be caused by:
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Graves disease
Graves disease
Graves disease is an autoimmune disorder that leads to an overactive thyroid gland (hyperthyroidism). An autoimmune disorder is a condition that occ...
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Toxic nodular goiter
or multinodular goiter
Toxic nodular goiter
Toxic nodular goiter involves an enlarged thyroid gland. The gland contains areas that have increased in size and formed nodules. One or more of th...
ImageRead Article Now Book Mark Article - Too much iodine in the body (due to receiving iodine contrast used during imaging tests, such as CT scan)
- Taking too much thyroid hormone medicine or prescribed natural or over-the-counter supplements that contain thyroid hormone
Use of certain medicines may also cause a lower-than-normal TSH level. These include glucocorticoids/steroids, dopamine, certain chemotherapy drugs, and opioid painkillers such as morphine.
Risks
Veins and arteries vary in size from one person to another and from one side of the body to the other. Obtaining a blood sample from some people may be more difficult than from others.
Other risks associated with having blood drawn are slight but may include:
- Excessive bleeding
- Fainting or feeling lightheaded
- Hematoma (blood buildup under the skin)
- Infection (a slight risk any time the skin is broken)
References
Salvatore D, Davies TF, Schlumberger MJ, Hay ID, Larsen PR. Thyroid physiology and diagnostic evaluation of patients with thyroid disorders. In: Melmed S, Polonsky KS, Larsen PR, Kronenberg HM, eds. Williams Textbook of Endocrinology . 13th ed. Philadelphia, PA: Elsevier; 2016:chap 11.
Weiss RE, Refetoff S. Thyroid function testing. In: Jameson JL, De Groot LJ, eds. Endocrinology: Adult and Pediatric . 7th ed. Philadelphia, PA: Elsevier Saunders; 2016:chap 78.
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Endocrine glands - illustration
Endocrine glands release hormones (chemical messengers) into the bloodstream to be transported to various organs and tissues throughout the body. For instance, the pancreas secretes insulin, which allows the body to regulate levels of sugar in the blood. The thyroid gets instructions from the pituitary to secrete hormones which determine the pace of chemical activity in the body (the more hormone in the bloodstream, the faster the chemical activity; the less hormone, the slower the activity).
Endocrine glands
illustration
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Pituitary and TSH - illustration
The pituitary secretes thyroid stimulating hormone (TSH), which stimulates the thyroid gland to secrete hormones that affect body metabolism.
Pituitary and TSH
illustration
-
Endocrine glands - illustration
Endocrine glands release hormones (chemical messengers) into the bloodstream to be transported to various organs and tissues throughout the body. For instance, the pancreas secretes insulin, which allows the body to regulate levels of sugar in the blood. The thyroid gets instructions from the pituitary to secrete hormones which determine the pace of chemical activity in the body (the more hormone in the bloodstream, the faster the chemical activity; the less hormone, the slower the activity).
Endocrine glands
illustration
-
Pituitary and TSH - illustration
The pituitary secretes thyroid stimulating hormone (TSH), which stimulates the thyroid gland to secrete hormones that affect body metabolism.
Pituitary and TSH
illustration
Review Date: 2/3/2016
Reviewed By: Brent Wisse, MD, Associate Professor of Medicine, Division of Metabolism, Endocrinology & Nutrition, University of Washington School of Medicine, Seattle, WA. Also reviewed by David Zieve, MD, MHA, Isla Ogilvie, PhD, and the A.D.A.M. Editorial team. Editorial update 07/20/2016.
