Euthyroid Sick Syndrome
(See also Overview of the Thyroid Gland.)
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, the thyroid hormone T4 (thyroxine, or tetraiodothyronine) is not converted normally to the active T3(triiodothyronine) hormone. 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. Because no problem exists with the thyroid gland, no treatment is needed. Laboratory tests show normal results once the underlying illness resolves.