Relationship between thyrotropin and thyroxine changes during recovery from severe hypothyroxinemia of critical illness

Abstract

In a prospective study of critically ill hypothyroxinemic patients, we assessed the relationship between serum TSH and T4 during the return of serum T4 normal during recovery. In this longitudinal study of 60 patients with a variety of critical illnesses, including burns, septicemia, and acute renal failure, serum T4 fell to less than 2.7 μg/dl (35 nmol/liter) in 24 patients, of whom 14 survived with return of T4 to normal. A rise in total T4 of more than 1.9 μg/dl (25 nmol/liter) within 96 h occurred 13 times in 10 patients, while 4 patients had slower increases in T4. All 13 episodes of rapid T4 rise [1.7 ± 0.8 (± SD) to 5.6 ± 2.1 μg/dl] were associated with a marked increase in serum TSH ..