euthyroid sick syndrome

• related: Endocrine
• aka nonthyroidal illness syndrome (NTIS)

• demographics: hospitalized and critically ill patients
• pathogenesis: illness suppress thyrotropin releasing hormone
• labs
  • suppressed but detectable TSH
  • undetectable TSH is not NTIS
  • Can sometimes have elevated TSH but not > 20 mU/L
  • T4 usually normal
  • T3 lower than normal due to decreased deiodinase activity
  • reverse T3 increases but biologically inactive
  • TBG decreases, lowering total T4 and T3 levels
• Treatment
  • Do not need to treat with levothyroxine
  • Recheck TSH 6 weeks after illness