Thyroid related
Nonthyroidal illness affecting thyroid function tests

Author: Nat Pernick, M.D. (see Authors page)

Revised: 3 February 2016, last major update March 2011

Copyright: (c) 2002-2016,, Inc.
Cite this page: Nonthyroidal illness affecting thyroid function tests. website. Accessed December 11th, 2018.
Definition / general
  • Also called euthyroid sick syndrome or low T4 syndrome
  • Seriously ill patients (sepsis, myocardial infarction, Angiology 2002;53:699) may have abnormal thyroid function tests without thyroid pathology
  • Due to reduced serum iodothyronine deiodinases (J Clin Endocrinol Metab 2003;88:3202)
  • Often caused by malnourishment (JPEN J Parenter Enteral Nutr 2006;30:415)
  • Initially these patients have low total T3 and free T3
  • Later thyroid binding globulin is disrupted causing low total T4
  • TSH is initially low to low-normal, then rises to normal or above normal as illness resolves, then returns to normal levels
  • TSH is suppressed by glucagon, dopamine and high doses of corticosteroids, which complicates interpretation
  • Common in medical intensive care unit (44%), and associated with poorer prognosis (Metabolism 2007;56:239)
Clinical images

  • In critical illness, inhibition of 5' deiodinase causes reduced T3 and increased reverse T3 levels