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Definition

Thyroid function tests are used to check whether your thyroid is working normally.

The most common thyroid function tests are:

  • Total T4 (the free hormone and the hormone bound to carrier proteins) 
  • Free T4 (the main thyroid hormone in your blood -- a precursor for T3)
  • TSH (the hormone from the pituitary gland that stimulates the thyroid to produce T4)
  • T3 (the active form of the hormone -- T4 is converted to T3)

Other thyroid tests include:

  • T3 resin uptake (an older test that is rarely used now)
  • Thyroid uptake and scan
  • Thyroid binding globulin
  • Thyroglobulin

The vitamin biotin (B7) can affect the results of many thyroid hormone tests. If you take biotin, talk to your provider before you have any thyroid function tests.

Review Date: 2/22/2018
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, Medical Director, Brenda Conaway, Editorial Director, and the A.D.A.M. Editorial team.

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