Serum 3,3′,5′-triiodothyronine (rT3) and 3,5,3′-triiodothyronine/rT3 are prognostic markers in critically ill patients and are associated with postmortem tissue deiodinase activities

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 T-3 and high rT(3). 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, rT(3) was higher and T-3/rT(3) 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 rT(3) and 2.9 for T-3/rT(3). TSH, T-4, and T-3 were lower in nonsurvivors fromd 5 until LD (P < 0.001). TSH, T-4, T-3, and T-3/rT(3) increased over time in survivors, but decreased or remained unaltered in nonsurvivors. Liver D1 activity was positively correlated with LD serum T-3/rT(3) (R = 0.83, P < 0.001) and negatively correlated with rT(3) (R = -0.69, P < 0.001). Both liver and skeletal muscle D3 activity were positively correlated with LD serum rT(3) (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, rT(3) and T-3/rT(3) were already prognostic for survival on d 1. On d 5, T-4, T-3, but also TSH levels are higher in patients who will survive. Serum rT(3) and T-3/rT(3) were correlated with postmortem tissue deiodinase activities.