Euthyroid Sick Syndrome - Inpatient Thyroid Function Tests
If thyroidal illness is suspected, TSH alone is inadequate – should also test for FT4 and T3. Half-lives: TSH 1hr, T4 7d, T3 1d.
Sick Euthyoid: Alterations in thyroid function due to nonthyroidal illness rather than 1o endocrine disorder; may be adaptive (anticatabolic); no indication to treat; most likely cause of abnormal TFTs among inpatients.
• Typical pattern: (1) Acute illness: ↓↓↓T3, ↓T4, ↓/nl FT4, ↓/nl TSH. (2) Recovery phase: ↑ TSH → recovery of T4, T3.
• Sequential FT4 should ↑ in recovering sick euthyroid but remains low in 1o hypothyroid. rT3 can differentiate central
hypothyroidism (↓) from sick euthyroid (↑), but rarely needed. FT3 is useless except to dx hyperthyroidism w/ altered TBG.
• NB: Undectable TSH (<0.01) suggests true hyperthyroidism, and TSH>20 + Low T4 suggests true hypothyroidism.
Biotin supplementation can interfere with TSH and other assays, ensure pt off biotin x 1week before testing
↓ TSH also seen with glucocorticoids, dopamine, dobutamine, octreotide, ↑ β-HCG levels
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