Suppression of the thyrotropin response to thyrotropin-releasing hormone and its association with severity of critical illness.

Abstract

To study whether the suppression of the thyrotropin (thyroid-stimulating hormone, TSH) response to thyrotropin-releasing hormone (TRH) correlates with severity of illness and death in patients with nonthyroidal critical illness. Prospective study. Intensive care unit (ICU) of a university hospital. Forty-one critically ill patients without thyroid disease with multiple organ failure who were admitted to the ICU. The TSH response to TRH was tested within 24 hrs of ICU admission. Blood samples were obtained just before, and at 15, 30, 60, 90, and 120 mins after 500-micrograms injection of synthetic TRH. Triiodothyronine, free-triiodothyronine, thyroxine, free-thyroxine and TSH concentrations were measured in the samples obtained just before TRH injection. Acute Physiology and Chronic Health Evaluation (APACHE II) scores and Sepsis scores were calculated based on the data obtained within 24 hrs of ICU admission. Individual variables were compared between survivors and nonsurvivors. The APACHE II scores and Sepsis scores of nonsurvivors were significantly higher than those scores of survivors. The overall occurrence of suppressed TSH response to TRH was 88%. Peak TSH concentration of the TSH response was significantly lower in nonsurvivors than in survivors. Serial measurement of the TSH response showed that nonsurvivors experienced a decrease in peak TSH concentration from 1.55 +/- 0.78 to 0.55 +/- 0.30 microIU/mL; in survivors, it increased from 2.10 +/- 0.26 to 7.38 +/- 1.83 microIU/mL. Conversely, the basal TSH concentration did not change in either survivors or nonsurvivors. The "severity" of illness of nonsurvivors remained high; their mean APACHE II score varied from 20.0 +/- 1.9 to 22.1 +/- 1.3 and the mean Sepsis score varied from 20.0 +/- 4.3 to 25.4 +/- 4.0, while the same scores for survivors decreased significantly (p < .05): their APACHE II score decreased from 16.2 +/- 0.7 to 7.6 +/- 2.0 and the Sepsis score went from 14.0 +/- 1.9 to 6.0 +/- 1.6. In critically ill patients with multiple organ failure, suppression of the TSH response to TRH frequently occurs and correlates with severity of illness and outcome. Our data indicate that measurement of the TSH response is helpful in evaluating the severity of illness and prognosis for critically ill patients.