Thyroid Function in Nonthyroidal Illnesses

doi:10.1059/0003-4819-98-6-946

Thyroid Function in Nonthyroidal Illnesses

Los Angeles, California

Abstract

Alterations in thyroid physiology and thyroid function tests occur in some patients with nonthyroidal illnesses. Low concentrations of serum triiodothyronine (T3) usually occur in nonthyroidal illnesses and are attributable largely to reduced extrathyroidal conversion of thyroxine (T4) to T3. Concentrations of serum total T4 may be low, normal, or high; alterations in serum binding of T4 explain the abnormality in most cases. Concentrations of serum reverse T3 are usually high because metabolic clearance is reduced. Whether patients with nonthyroidal illnesses with low T4 or T3, or both, are hypothyroid is uncertain; concentrations of free T4 have been estimated as low, normal, or high using different methods. Serum thyroidstimulating hormone is typically normal. Low concentrations of T3 or T4, or both, in nonthyroidal illnesses may have a homeostatic significance. Low serum concentrations of T4 correlate with poor prognosis in nonthyroidal illnesses. Inhibitors of thyroid hormone binding and phagocytosis are present in normal tissues. Leakage of the inhibitors into the circulation may lower serum concentrations of T4 on one hand and compromise critical host defenses on the other.

Article and Author Information

▸ An edited transcription of an Interdepartmental Conference arranged by the Department of Medicine of the UCLA School of Medicine, Los Angeles, California.
▸ Authors who wish to cite a section of this conference and specifically indicate its author can use this example of the form of the reference:

HERSHMAN JM. Free thyroxine in nonthyroidal illness, pp. 947-50. In: CHOPRA IJ, moderator. Thyroid function in nonthyroidal illnesses. Ann Intern Med. 1983;98:946-57.
Grant support: in part by grants AM 16155, AM 25744, AM 11727, AM 29955 from the U. S. Public Health Service; General Clinical Research Grant RR-43; Basil O'Connor Award from the March of Dimes Birth Defects Foundations; and Medical Research Funds of the Veterans Administration.
▸ Requests for reprints should be addressed to Inder J. Chopra, M.D.; Department of Medicine, Division of Endocrinology, UCLA School of Medicine; Los Angeles, CA 90024.