Sick euthyroid syndrome - thyroid function test pattern and mechanism
Core concept
- Sick euthyroid syndrome (non-thyroidal illness syndrome) = abnormal TFTs in a patient with acute severe illness but no intrinsic thyroid disease
- Mechanism: acute illness/cytokines (IL-6, TNF) -> dec Type 1 deiodinase activity -> reduced peripheral T4->T3 conversion, and inc reverse T3 (inactive) production
- Also central suppression of TSH/TRH pulsatility in critical illness, and reduced thyroid-binding globulin
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