Changes in thyroid hormone levels during illness

Severity of illnessTSHTotal T3Free T4Reverse T3Probable cause
MildNo changeMildly decreasedNo changeMildly increasedMildly decreased D2, D1
ModerateNo change or mildly decreasedDecreasedNo change or mild increase or decreaseIncreasedDecreased D2, D1, possibly mildly increased D3
SevereDecreasedMarkedly decreasedMildly decreasedMildly increasedDecreased D2, D1, possibly mildly increased D3
RecoveryMildly increasedMildly decreasedMildly decreasedMildly increasedUnknown
  • D1 through D3 = iodothyronine deiodinases; T3, triiodothyronine; T4 = thyroxine; TSH = thyroid-stimulating hormone (thyrotropin).

  • Adapted from Salvatore D, Davies TF, Schlumberger M, Hay ID, Larsen PR. Thyroid physiology and diagnostic evaluation of patients with thyroid disorders. In: Melmed S, Polonsky KS, Larsen PR, Kronenberg HM, eds. Williams Textbook of Endocrinology. 13th ed. Philadelphia, PA; Elsevier; 2016:334–368, copyright 2016, with permission from Elsevier.