Introduction Apparent alterations to thyroid hormone level with normal thyroid gland function 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 Likely a response to an acute/chronic illness cancer cardiac disease (MI, CHF) CRF sepsis Evaluation Serology ↓ total serum T4/T3 normal serum TSH ↑ reverse T3