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Euthyroid Sick Syndrome — RACP Adult Medicine MCQ

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ModerateEndocrinologyEuthyroid Sick SyndromeRACP Adult Medicine

A 65-year-old critically ill man in ICU with septic shock has thyroid function tests: TSH 0.3 mU/L (low-normal/mildly low), free T4 12 pmol/L (low-normal), free T3 1.5 pmol/L (low). Reverse T3 is elevated. He has no prior thyroid disease. What is the most likely interpretation?

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Correct answer: B — Euthyroid sick syndrome (non-thyroidal illness)

Low T3 with low-normal T4, mildly suppressed TSH, and elevated reverse T3 in a critically ill patient without thyroid disease is euthyroid sick syndrome (non-thyroidal illness). Peripheral conversion of T4 to T3 is reduced (increased conversion to inactive reverse T3). Thyroid hormone replacement is NOT indicated — it does not improve outcomes and may be harmful. TFTs normalise on recovery.

Reference: eTG Endocrine – 2024 – Non-Thyroidal Illness; ESA 2024