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Thyroid Hormone Tests

What Affects the Test

Reasons you may not be able to have the test or why the results may not be helpful include:

What To Think About

  • Because false-positive results can occur when testing a newborn for congenital hypothyroidism, the thyroid hormone tests may be repeated a few days after initial testing. If the results are still abnormal and congenital hypothyroidism is suspected, additional testing is done.
  • Other blood tests are often used to check how well the thyroid gland is working.
    • Thyroid-stimulating hormone (TSH) test measures the amount of TSH in the blood and is considered the most reliable way to find a thyroid problem. If the TSH test is abnormal, other thyroid hormone tests such as a T3 or T4 may be done. For more information, see the topic Thyroid-Stimulating Hormone.
    • Thyroid antibodies test measures the presence of antibodies against thyroid tissue. Antibodies may mean that you have an autoimmune disease such as Hashimoto's thyroiditis or Graves' disease.
    • Thyroxine-binding globulin (TBG) test. TBG is an important protein in the blood that carries the thyroid hormones T3 and T4. TBG testing is not done very often.
  • Other tests used to investigate problems with the thyroid gland include:

Citations

  1. U.S. Preventive Services Task Force (2008). Screening for congenital hypothyroidism: Reaffirmation recommendation statement. Available online: http://www.uspreventiveservicestaskforce.org/uspstf08/conhypo/conhyprs.htm.

  2. Fischbach FT, Dunning MB III, eds. (2009). Manual of Laboratory and Diagnostic Tests, 8th ed. Philadelphia: Lippincott Williams and Wilkins.

Other Works Consulted

  • Chernecky CC, Berger BJ (2008). Laboratory Tests and Diagnostic Procedures, 5th ed. St. Louis: Saunders.

  • Fischbach FT, Dunning MB III, eds. (2009). Manual of Laboratory and Diagnostic Tests, 8th ed. Philadelphia: Lippincott Williams and Wilkins.

WebMD Medical Reference from Healthwise

Last Updated: August 07, 2012
This information is not intended to replace the advice of a doctor. Healthwise disclaims any liability for the decisions you make based on this information.

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