Introduction Apparent alterations thyroid hormone level with normal thyroid gland funciton peripheral activity of outer ring deiodinase is ↓ normally converts T4 to T3 peripheral activity of inner ring deiodinase is ↑ normally converts T4 to reverse T3 Associated with cancer cardiac disease (MI, CHF) CRF sepsis Evaluation Serology ↓ total serum T4/T3 ↓ serum TSH ↑ reverse T3 Management Treat and manage primary underlying illness Likely no need to start thyroid hormone replacement (controversial) Recheck thyroid function studies after illness has resolved