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Home , Thyroid hormones

Thyroid Tests

National Endocrine and Metabolic Diseases Information Service

What is the ? (TSH), which is made by the pituitary gland in the , regulates thyroid The thyroid is a 2-inch-long, butterfly-shaped production. When thyroid hormone levels gland weighing less than 1 ounce. Located in the are low, the pituitary releases in the front of the neck below the larynx, or more TSH. When thyroid hormone levels voice box, it has two lobes, one on either side are high, the pituitary decreases TSH of the windpipe. production. The thyroid is one of the glands that make up the . The glands of the endocrine system produce and store Pituitary and release them into the gland bloodstream. The hormones then travel through the body and direct the activity of the body’s cells.

What is the role of ? Thyroid hormones regulate —the way the body uses energy—and affect nearly TSH every organ in the body. Thyroid hormones also affect brain development, breathing, and nervous system functions, body temperature, muscle strength, skin dryness, Thyroid menstrual cycles, weight, and cholesterol levels. The thyroid makes two thyroid hormones:

• thyroxine (T4) T3-T4

• (T3) When thyroid hormone levels in the blood are low, Only a small amount of T3 in the blood the pituitary releases more TSH. When thyroid comes from the thyroid. Most T3 comes hormone levels are high, the pituitary decreases TSH from cells all over the body, where it is made production. from T4. Thyroid-stimulating hormone Why do health care A blood test involves drawing blood at a health care provider’s office or a commercial providers perform facility and sending the sample to a lab thyroid tests? for analysis. Blood tests assess thyroid Health care providers perform thyroid tests function by measuring TSH and thyroid to assess how well the thyroid is working. hormone levels, and by detecting certain The tests are also used to diagnose and help autoantibodies present in autoimmune find the cause of thyroid disorders such as . Autoantibodies are and : molecules produced by a person’s body that mistakenly attack the body’s own tissues. • Hyperthyroidism is a disorder caused by too much thyroid hormone in the Many complex factors affect thyroid function bloodstream, which increases the speed and hormone levels. Health care providers of bodily functions and leads to weight take a patient’s full medical history into loss, sweating, rapid , and high account when interpreting thyroid function blood pressure, among other symptoms. tests. • Hypothyroidism is a disorder that TSH Test occurs when the thyroid doesn’t make A health care provider usually performs the enough thyroid hormone for the TSH blood test first to check how well the body’s needs. Without enough thyroid thyroid is working. The TSH test measures hormone, many of the body’s functions the amount of TSH a person’s pituitary is slow down. People may have symptoms secreting. The TSH test is the most accurate such as fatigue, weight gain, and cold test for diagnosing both hyperthyroidism and intolerance. hypothyroidism. Generally, a below-normal Read more about thyroid disorders in level of TSH suggests hyperthyroidism. Hyperthyroidism and Hypothyroidism at An abnormally high TSH level suggests www.endocrine.niddk.nih.gov. hypothyroidism. The TSH test detects even tiny amounts of What blood tests do health TSH in the blood. Normally, the pituitary care providers use to check boosts TSH production when thyroid hormone levels in the blood are low. The a person’s thyroid function? thyroid responds by making more hormone. A health care provider may order several Then, when the body has enough thyroid blood tests to check thyroid function, hormone circulating in the blood, TSH including the following: output drops. The cycle repeats continuously • TSH test to maintain a healthy level of thyroid hormone in the body. In people whose • T4 tests thyroid produces too much thyroid hormone, the pituitary shuts down TSH production, • T3 test leading to low or even undetectable TSH • thyroid-stimulating immunoglobulin levels in the blood. (TSI) test • antithyroid antibody test, also called the antibody test (TPOab)

2 Thyroid Tests In people whose thyroid is not functioning T3 Test normally and produces too little thyroid If a health care provider suspects hormone, the thyroid cannot respond hyperthyroidism in a person who has a normally to TSH by producing thyroid normal FT4 level, a T3 test can be useful hormone. As a result, the pituitary keeps to confirm the condition. In some cases of making TSH, trying to get the thyroid to hyperthyroidism, FT is normal yet free T respond. 4 3 (FT3) is elevated, so measuring both T4 and If results of the TSH test are abnormal, a T3 can be useful if a health care provider person will need one or more additional tests suspects hyperthyroidism. The T3 test is to help find the cause of the problem. not useful in diagnosing hypothyroidism because levels are not reduced until the T4 Tests hypothyroidism is severe. The thyroid primarily secretes T4 and only a TSI Test small amount of T3. T4 exists in two forms: Thyroid-stimulating immunoglobulin is an • T4 that is bound to in the blood autoantibody present in Graves’ disease. TSI and is kept in reserve until needed mimics TSH by stimulating the thyroid cells, • a small amount of unbound or “free” causing the thyroid to secrete extra hormone. T4 (FT4), which is the active form of the The TSI test detects TSI circulating in the hormone and is available to enter body blood and is usually measured tissues when needed • in people with Graves’ disease when the

A high level of total T4—bound and FT4 diagnosis is obscure together—or FT4 suggests hyperthyroidism, • during pregnancy and a low level of total T4 or FT4 suggests hypothyroidism. • to find out if a person is in remission, or no longer has hyperthyroidism and its Both pregnancy and taking oral symptoms contraceptives increase levels of binding in the blood. In either of these cases, Antithyroid Antibody Test although a woman may have a high total T4 Antithyroid antibodies are markers in level, she may not have hyperthyroidism. the blood that are extremely helpful in Severe illness or the use of —a diagnosing Hashimoto’s disease. Two class of that treat asthma, principal types of antithyroid antibodies are arthritis, and skin conditions, among other health problems—can decrease binding • anti-TG antibodies, which attack protein levels. Therefore, in these cases, the a protein in the thyroid called total T4 level may be low, yet the person does not have hypothyroidism. • anti-thyroperoxidase, or anti-TPO, antibodies, which attack an in thyroid cells called thyroperoxidase

3 Thyroid Tests What do thyroid test results What imaging tests do tell health care providers? health care providers use to Health care providers look at thyroid test diagnose and find the cause results in people with hyperthyroidism or of thyroid disorders? hypothyroidism to find the underlying cause of their thyroid disorder. The following A health care provider may use one or a tables illustrate what test results may show combination of imaging tests, such as an based on the type of thyroid problem. ultrasound of the thyroid, a computerized tomography (CT) scan, or nuclear medicine tests, to diagnose and find the cause of Table 1. Typical thyroid function test results: thyroid disorders. Hyperthyroidism • Ultrasound. Ultrasound uses a device, Test called a transducer, that bounces safe, painless sound waves off organs to Cause Radioactive create an image of their structure. A TSH T3/T4 TSI Uptake Test specially trained technician performs the procedure in a health care Graves’ disease ↓ ↑ + ↑ provider’s office, an outpatient center, Thyroiditis (with or a hospital, and a radiologist—a ↓ ↑ − ↓ hyperthyroidism) doctor who specializes in medical Thyroid nodules imaging—interprets the images; a ↓ ↑ − ↑ or Normal (hot, or toxic) patient does not need anesthesia. The images can show the size and texture Key:  = Above Normal + = Positive ↑ of the thyroid, as well as a pattern of ↓= Below Normal − = Negative typical autoimmune inflammation. The images can also show nodules or Table 2. Typical thyroid function test results: growths within the gland that suggest a Hypothyroidism malignant tumor. Test • CT scan. CT scans use a combination of x rays and computer technology to Cause Antithyroid TSH T /T Antibody create images. For a CT scan, a health 3 4 care provider may give the patient a Hashimoto’s disease ↓ or solution to drink and an injection of a (thyroiditis, early ↑ + Normal special dye, called contrast medium. stage) CT scans require the patient to lie on Hashimoto’s disease a table that slides into a tunnel-shaped (thyroiditis, later ↑ ↓ + device where the x rays are taken. An stage) x-ray technician performs the procedure Pituitary ↓ ↓ − in an outpatient center or a hospital, abnormality and a radiologist interprets the images. Key: ↑ = Above Normal + = Positive The patient does not need anesthesia. ↓= Below Normal − = Negative CT scans are usually not needed to

4 Thyroid Tests diagnose thyroid disease; however, A device called a gamma camera is health care providers will use them to suspended over the table or may be view a large goiter. Also, a CT scan located within a large, tunnel-shaped will often show a when device that resembles a CT scanner. a person is having the scan for other The gamma camera detects the health problems. radioactive material and sends images to a computer that show how and where Nuclear medicine tests. Nuclear medicine the radioactive substance has been tests of the thyroid include a thyroid scan distributed in the thyroid. Nodules that and a radioactive iodine uptake test. produce too much thyroid hormone— People often have to follow a low iodine called “hot,” or toxic, nodules—show diet prior to having the tests. Read more up clearly because they absorb more about a low iodine diet from the American radioactive material than normal Thyroid Association at www.thyroid.org/ thyroid tissue. Graves’ disease shows faq-low-iodine-diet. up as a spread-out, overall increase in • Thyroid scan. A thyroid scan is a type radioactivity rather than an increase in a of nuclear medicine imaging. Nuclear localized spot. medicine uses small amounts of Even though the amount of radiation radioactive material to create a picture used in this test is small, women who of an organ and give information about are pregnant or breastfeeding should the organ’s structure and function. not have this test because of the risks A thyroid scan is used to look at the of exposing the fetus or the baby to size, shape, and position of the gland. radiation. This test can help find the cause of hyperthyroidism and check for thyroid • Radioactive iodine uptake test. The nodules. The scan also can help a radioactive iodine uptake test, also health care provider evaluate thyroid known as a thyroid uptake, is a nuclear nodules; however, it does not confirm medicine test used to evaluate the whether the nodules are cancerous or function of the thyroid and find the benign. cause of a patient’s hyperthyroidism. A specially trained technician performs A whole-body thyroid scan is used for the procedure in an outpatient center or people who have had . a hospital, and a radiologist interprets The test measures the amount of the images; a patient does not need iodine the thyroid collects from the anesthesia. For the scan, radioactive bloodstream in a given time period. iodine or radioactive technetium is The thyroid uptake is not used to assess injected into the patient’s vein or hypothyroidism. swallowed in liquid or capsule form. A specially trained technician performs The scan takes place 30 minutes after the test in an outpatient center or a an injection or 6 to 24 hours after the hospital, and a radiologist interprets radioactive substance is swallowed. The the images; a patient does not need patient lies on an exam table for the anesthesia. For this test, the patient scan, which takes about 30 minutes. swallows a small amount of radioactive

5 Thyroid Tests iodine in liquid or capsule form. After Even though the amount of radiation 4 to 6 hours and again at 24 hours, the used in this test is small, women who patient returns to the testing center, are pregnant or breastfeeding should where the technician measures the not have this test because of the risks of amount of radioactive iodine taken exposing the fetus or infant to radiation. up by the thyroid. The measurement is taken with a small device called What tests do health care a gamma probe, which resembles a microphone. The gamma probe is providers use if a thyroid positioned near the patient’s neck over nodule is found? the thyroid. Measurement takes only a If a health care provider feels a nodule in few minutes and is painless. a patient’s neck during a physical exam In the diagnosis of hyperthyroidism, or detects one during imaging tests of the a high thyroid uptake reading usually thyroid, a fine needle aspiration biopsy may indicates an overactive thyroid that be done to confirm whether the nodule is produces too much thyroid hormone, cancerous or benign. as seen in Graves’ disease or a A fine needle aspiration biopsy of the thyroid condition called toxic nodular goiter, involves taking cells from the thyroid for an enlargement of the thyroid. A low examination with a microscope. The health thyroid uptake reading suggests the care provider with experience in needle thyroid is not overactive. aspirations performs the biopsy in his or her Several thyroid disorders that cause office, an outpatient center, or a hospital; he inflammation of the thyroid, or or she may use to numb the area. thyroiditis, may cause leakage of The patient may feel mild discomfort during thyroid hormone and iodine out of the the test and the biopsy site may be tender for thyroid into the bloodstream, which 1 to 2 days. can lead to high T4 levels. When the For this test, the patient lies back with thyroid is inflamed, it does not take up support under the shoulders so the neck can the radioactive iodine given as part of be extended and bent back slightly. The the thyroid uptake test. For example, health care provider inserts a small, thin hyperthyroidism seen in Graves’ disease needle attached to a syringe into the thyroid would be marked by high blood T4 nodule and uses ultrasound to guide its and a high thyroid uptake reading. In insertion. Samples of the cells in the nodule thyroiditis, temporary hyperthyroidism are drawn through the needle and sent to may exist because of the release a lab to be examined by a pathologist—a of T4 into the blood; however, the doctor who specializes in diagnosing thyroid uptake reading is low because diseases. The health care provider may need of the inflammation. Temporary to take several samples. Once the biopsy is hyperthyroidism in thyroiditis is often complete, a bandage is placed on the area to followed by a period of hypothyroidism lower the chance of bleeding. before the thyroid heals.

6 Thyroid Tests Points to Remember • If a health care provider feels a nodule in a patient’s neck during a • The thyroid is one of the glands physical exam or detects one during that make up the endocrine system. imaging tests of the thyroid, a fine Thyroid hormones affect metabolism, needle aspiration biopsy may be done brain development, breathing, heart to confirm whether the nodule is and nervous system functions, body cancerous or benign. temperature, muscle strength, skin dryness, menstrual cycles, weight, and cholesterol levels. Hope through Research • The TSH test is the most accurate test The National Institute of and for diagnosing both hyperthyroidism Digestive and Diseases (NIDDK) and hypothyroidism. conducts and supports research into many kinds of disorders, including thyroid • Health care providers perform thyroid disease. Researchers are investigating function tests to assess how well the the development, signs and symptoms, thyroid is working. The tests also are and genetics of thyroid function disorders used to diagnose and help find the cause to better understand thyroid diseases. of thyroid disorders. Scientists continue to study treatment • Hyperthyroidism is caused by too much options for hyperthyroidism, hypothyroidism, thyroid hormone in the bloodstream, and other thyroid diseases. which increases the speed of bodily Clinical trials are research studies involving functions and leads to weight loss, people. Clinical trials look at safe and sweating, rapid heart rate, and high effective new ways to prevent, detect, or blood pressure, among other symptoms. treat disease. Researchers also use clinical • Hypothyroidism is a disorder that trials to look at other aspects of care, such occurs when the thyroid doesn’t make as improving the quality of life for people enough thyroid hormone for the with chronic illnesses. To learn more about body’s needs. Without enough thyroid clinical trials, why they matter, and how to hormone, many of the body’s functions participate, visit the NIH Clinical Research slow down. People may have symptoms Trials and You website at www.nih.gov/health/ such as fatigue, weight gain, and cold clinicaltrials. For information about current intolerance. studies, visit www.ClinicalTrials.gov. • A health care provider may order several blood tests to check thyroid You may also find additional information about this function. topic by visiting MedlinePlus at www.medlineplus.gov. • A health care provider may use one or This publication may contain information about medications and, when taken as prescribed, a combination of imaging tests, such as the conditions they treat. When prepared, this an ultrasound of the thyroid, a thyroid publication included the most current information scan, or a radioactive iodine uptake available. For updates or for questions about any medications, contact the U.S. Food and test, to diagnose and find the cause of Administration toll-free at 1–888–INFO–FDA thyroid disorders. (1–888–463–6332) or visit www.fda.gov. Consult your health care provider for more information.

7 Thyroid Tests For More Information National Endocrine American Association of Clinical and Metabolic Diseases Endocrinologists Information Service 245 Riverside Avenue, Suite 200 Jacksonville, FL 32202 6 Information Way Phone: 904–353–7878 Bethesda, MD 20892–3569 Fax: 904–353–8185 Phone: 1–888–828–0904 Internet: www.aace.com TTY: 1–866–569–1162 Fax: 703–738–4929 American Thyroid Association Email: [email protected] 6066 Leesburg Pike, Suite 550 Internet: www.endocrine.niddk.nih.gov Falls Church, VA 22041 Phone: 703–998–8890 The National Endocrine and Metabolic Fax: 703–998–8893 Diseases Information Service is an Email: [email protected] information dissemination service of the Internet: www.thyroid.org National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK). The The Endocrine Society NIDDK is part of the National Institutes of 8401 Connecticut Avenue, Suite 900 Health, which is part of the U.S. Department Chevy Chase, MD 20815–5817 of Health and Human Services. Phone: 1–888–363–6274 or 301–941–0200 Fax: 301–941–0259 The NIDDK conducts and supports Email: [email protected] biomedical research. As a public service, the Internet: www.endo-society.org NIDDK has established information services to increase knowledge and understanding Graves’ Disease and Thyroid Foundation about health and disease among patients, P.O. Box 2793 health professionals, and the public. Rancho Santa Fe, CA 92067 Phone: 1–877–643–3123 Fax: 1–877–643–3123 This publication is not copyrighted. The NIDDK encourages users of this publication to duplicate and Email: [email protected] distribute as many copies as desired. Internet: www.gdatf.org This publication is available at Hormone Health Network www.endocrine.niddk.nih.gov. Phone: 1–800–HORMONE (1–800–467–6663) Email: [email protected] Internet: www.hormone.org

Acknowledgments Publications produced by the NIDDK are carefully reviewed by both NIDDK scientists and outside experts. This publication was originally reviewed by Lewis Braverman, M.D., Boston Medical Center, and Leonard Wartofsky, M.D., M.A.C.P., Washington Hospital Center. NIH Publication No. 14–6284 February 2014

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