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Information on Thyroid Laboratory Tests

written by: Leigh A. Zaykoski•edited by: Paul Arnold•updated: 3/23/2009

Information on thyroid laboratory tests can help you understand thyroid blood tests and thyroid function tests. Read this article to find out about the TSH, T4, and T3 thyroid blood tests.

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    If you have a thyroid disorder, you may be experiencing a wide range of symptoms including fatigue, weight gain, and weight loss. In order to find out if you have a thyroid condition, and determine which condition you have, your doctor may run one or more laboratory tests. Use this information on thyroid laboratory tests to learn about the tests your doctor may order and how they are used as a diagnostic tool.

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    Thyroid Blood Tests: TSH

    TSH is also known as thyrotropin or thyroid-stimulating hormone. Doctors will check a TSH level to diagnose or rule out an overactive or underactive thyroid as well as to monitor the effects of drugs on a patient. This is one of the thyroid function tests that can also be used to monitor fertility problems in women. Blood is drawn from a vein in the arm and analyzed in a laboratory setting. If the result is high, the patient may have an underactive thyroid gland. Low TSH levels can incidcate that someone has an overactive thyroid gland or that someone's thyroid hormone medication dosage needs to be adjusted.

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    Thyroid Function Tests: Total T4 and Free T4

    Two other thyroid blood tests that can be used are the total T4 and free T4. The total T4 test has been used to diagnose hyper- and hypothyroidism for many years. However, the test results can be affected by the amount of protein in the blood since thyroxine can bind with protein. The free T4 test is more accurate at determing thyroxine levels because it is not affected by protein. This is one of the function thyroid tests that can be used to monitor patients who have goiters or problems with fertility. High results may point to an overactive thyroid gland, while low results may indicate hypothyroidism.

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    Thyroid Blood Tests: Total T3 and Free T3

    When you're looking for information on thyroid laboratory tests, another test you will want to research is the T3. This thyroid blood test measures the level of triiodothyronine and can help to determine if someone has a thyroid condition. Like the total T4 test, the total T3 test can be affected by the amount of protein in a person's blood. The free T3 is not affected by protein levele, so it may be a more accurate test. These thyroid function tests are ordered when someone has other abnormal thyroid blood test results or if someone needs to be monitored while taking medication for a thyroid condition. It is important that you let your doctor know if you are taking estrogen or birth control pills, as these can affect the results of the total T3 test.

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    Further Information on Thyroid Laboratory Tests

    For more information on thyroid laboratory tests, visit Lab Tests Online and view the Thyroid Panel page to learn how why these tests and performed and what the results may mean.