Serum 3,3′,5′-Triiodothyronine (rT 3 ) and 3,5,3′-Triiodothyronine/rT 3 Are Prognostic Markers in Critically Ill Patients and Are Associated with Postmortem Tissue Deiodinase Activities

Abstract

INTRODUCTION AND METHODS: Critical illness is associated with reduced TSH and thyroid hormone secretion, and with changes in peripheral thyroid hormone metabolism, resulting in low serum T3 and high rT3. In 451 critically ill patients who received intensive care for more than 5 d, serum thyroid parameters were determined on d 1, 5, 15, and last day (LD). All patients had been randomized for intensive or conventional insulin treatment. Seventy-one patients died, and postmortem liver and skeletal muscle biopsies were obtained from 50 of them for analysis of deiodinase (D1-3) activities. RESULTS: Insulin treatment did not affect thyroid parameters. On d 1, rT3 was higher and T3/rT3 was lower in nonsurvivors as compared with survivors (P = 0.001). Odds ratio for survival of the highest vs. the lowest quartile was 0.3 for rT3 and 2.9 for T3/rT3. TSH, T4, and T3 were lower in nonsurvivors from d 5 until LD (P < 0.001). TSH, T4, T3, and T3/rT3 increased over time in survivors, but decreased or remained unaltered in nonsurvivors. Liver D1 activity was positively correlated with LD serum T3/rT3 (R = 0.83, P < 0.001) and negatively correlated with rT3 (R = -0.69, P < 0.001). Both liver and skeletal muscle D3 activity were positively correlated with LD serum rT3 (R = 0.32, P = 0.02 and R = 0.31, P = 0.03). CONCLUSION: In critically ill patients who required more than 5 d of intensive care, rT3 and T3/rT3 were already prognostic for survival on d 1. On d 5, T4, T3, but also TSH levels are higher in patients who will survive. Serum rT3 and T3/rT3 were correlated with postmortem tissue deiodinase activities.