No Significance of the Free Cortisol Index Compared to Total Cortisol in Critically Ill Patients

ABSTRACT

BACKGROUND: Some patients exhibit an inadequate response of cortisol to stressful conditions; this state is known as critical illness-related corticosteroid insufficiency. These patients have low serum binding protein concentrations, thereby suggesting that total serum cortisol may not be reflective of circulating cortisol activity. As the free cortisol index (FCI = total cortisol/corticosteroid-binding globulin) has been correlated with serum free cortisol, we measured FCI in Korean patients for the first time. In this study, we attempted to determine whether FCI was superior to total cortisol in predicting 30-day mortality. METHODS: We recruited 65 critically ill patients with relatively high Acute Physiology, Age and Chronic Health Evaluation (APACHE III) scores. Fourteen patients with pituitary disease but normal pituitary function were recruited from outpatient clinics. Total cortisol and corticosteroid-binding globulin were measured in patients and controls during the short Synacthen test. RESULTS: The basal cortisol level and basal FCI level were higher in patients (n = 65) than in healthy controls (P < 0.001, respectively). We found that total cortisol was strongly correlated with FCI (P < 0.001) in critically ill patients; however, neither total cortisol nor FCI were associated with 30-day mortality among patients. Only severe clinical criteria (such as APACHE-III scores and low albumin) were associated with 30-day mortality. CONCLUSION: Our results do not suggest that FCI is more accurate than total cortisol in predicting clinical outcomes in critically ill patients.