Merck Manual

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Euthyroid Sick Syndrome

By

Jerome M. Hershman

, MD, MS, David Geffen School of Medicine at UCLA

Last full review/revision Aug 2019| Content last modified Aug 2019
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In euthyroid sick syndrome, thyroid test results are abnormal even though the thyroid gland is functioning normally.

Euthyroid sick syndrome commonly occurs in people who have a severe illness other than thyroid disease. When people are sick or undernourished or have had surgery, less thyroid hormone T4 (thyroxine, or tetraiodothyronine) is converted to the active thyroid hormone, T3 (triiodothyronine). Large amounts of reverse T3, an inactive thyroid hormone, accumulate. Despite this abnormal conversion, the thyroid gland continues to function and to control the speed at which the body’s chemical functions proceed (metabolic rate) normally despite changes in some of the results of thyroid blood tests.

Because no problem exists with the thyroid gland, no treatment is needed. Laboratory tests show normal results once the underlying illness resolves.

NOTE: This is the Consumer Version. DOCTORS: Click here for the Professional Version
Click here for the Professional Version

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