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Medical Review - Articles by Medical Review Staff

Prepared March 1, 2006

Thyroid Hormone Testing

By Howell Johnson, M.D., Associate Medical Director

No single test can adequately reflect thyroid states under all circumstances.  Among possible problems are the recovery phase of non thyroid illness, states of resistance to thyroid hormone, thyrotropin producing tumors, thyroid states in acute psychiatric illness, early in thyrotoxicosis, subacute thyroiditis, and central (secondary) hypothyroidism.

Sensitive TSH has become the primary thyroid function test for stable, ambulatory subjects who lack pituitary or neuropsychiatric illness.  A sTSH result within the accepted reference range provides strong evidence for euthyroidism.  In most cases, thyroid hormone testing can be accomplished with sTSH testing alone.  This includes screening for thyroid hormone abnormalities and monitoring thyroid hormone therapy.

Free thyroxin (free T4) is necessary less frequently.  Indication, include use as a confirmatory test, assessing the severity of hyperthyroidism, and in diagnosing and managing central hypothyroidism.

Free triiodothyronine (free T3) is even less frequently necessary.  The primary indication for this test is diagnosing T3 thyrotoxicosis.

Testing for free T4 will be allowed for initial diagnosis of hyperthyroidism and for managing pituitary hypothyroidism.  Free T3 will be allowed for T3 thyrotoxicosis.

Testing for free T3 and free T4 for other indications will be reviewed for medical necessity.


  1. Jacobs and DeMott:  Laboratory Test Handbook, 5th Edition, Lexi-Comp Inc. Cleveland, Ohio, 2001
  2. ACP Medicine at http://www.acpmedicine.com.  WebMD Professional Publishing NY, NY 2005

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