Random serum free cortisol and total cortisol measurements in pediatric septic shock

Background The aim of the study was to examine the relationship between serum total cortisol (TC) and free cortisol (FC) levels in children with septic shock and the relationship of these levels with baseline illness severity. Methods A sub-study of a randomized controlled trial (RCT) of hydrocortisone vs. placebo in pediatric septic shock conducted in seven academic pediatric intensive care units (PICUs) in Canada on children aged newborn to 17 years. Thirty children with septic shock had serum sent for TC and FC measurement within 6 h of meeting the study eligibility criteria. Results Baseline FC and TC levels were strongly correlated with baseline Pediatric Risk of Mortality (PRISM) score (R2=0.759, p<0.001; R2=0.717, p<0.001) and moderately correlated with admission Vasotropic Inotropic Score (VIS) (R2=0.489, p<0.001; R2=0.316, p<0.001). Serum TC levels were highly correlated with FC levels (R2=0.92, p<0.001) and showed strong agreement (R2=0.98, p<0.001 on a Bland-Altman plot). The ratio of FC to TC moderately correlated with TC levels (R2=0.46, p<0.001) but did not correlate with baseline albumin levels (R2=0.19, p=0.13). Conclusions Random TC and FC levels are strongly correlated, show strong agreement and are reflective of illness severity in children with septic shock. As such, isolated FC measurement does not appear to provide added information relative to TC in acutely ill children with septic shock.