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Euthyroid Sick Syndrome

Meaning

A non-thyroidal illness syndrome characterized by abnormal thyroid hormone levels in the serum of patients who are critically ill or systemically stressed but whose thyroid gland itself is functionally normal. This condition, often termed Non-Thyroidal Illness (NTI), reflects an adaptive peripheral change in thyroid hormone metabolism rather than primary thyroid gland failure. It is a physiological response to acute illness, impacting metabolic regulation and overall endocrine status. This syndrome requires careful clinical differentiation from true primary hypothyroidism.