Preparation Methods to Measure Free Cortisol Evaluated

The assessment of free rather that total cortisol may be beneficial for the diagnosis of critical illness-related cortisol insufficiency.

Centrifugal ultrafiltration could provide timely free cortisol data that should correlate with the equilibrium dialysis technique when the free cortisol fractions are identically quantified by chemiluminescence immunoassay.

A prospective, multi-institutional, observational cohort investigation has been carried out involving seven pediatric intensive care units within the Eunice Kennedy Shriver National Institute of Child Health and Human Development Collaborative Pediatric Critical Care Research Network (Rockville, MD, USA). Blood samples from165 critically ill children across the spectrum of illness severity were analyzed. Temperature-controlled centrifugal ultrafiltration (CUF) was conducted using YM-30 membrane fitters and compared with equilibrium dialysis, the gold standard, using the Rapid Equilibrium Dialysis Device. The cortisol assays were performed at using the VITROS ECi Immunodiagnostic System (Ortho Clinical Diagnostics, Rochester, NY, USA) using enhanced chemiluminescence detection.

The time to derive plasma free cortisol concentrations after centrifugal ultrafiltration was approximately 2 hours compared with the 24 hours after the equilibrium dialysis fractionation with chemiluminescence immunoassay. When using the CUF with a 30,000 molecular weight cutoff (Millipore, Billerica, MA, USA) the mean plasma free cortisol was 4.1 ± 6.7 µg/dL, representing an average of 15.2 ± 9.4% of total cortisol. Nearly 60% of subjects exhibited free cortisol of less than 2 μg/dL, and 30% had less than 0.8 µg/dL, which are previously suggested threshold concentrations for defining critical illness-related cortisol insufficiency. A strong correlation was demonstrated for the plasma-free cortisol concentrations when comparing CUF and the Pierce Protein Research Product's equilibrium dialysis fractionation (Thermo Fisher Scientific Inc, Rockford, IL, USA).

The authors concluded that the determination of CUF fractionated free cortisol was fast and results correlated highly with equilibrium dialysis fractionated free cortisol. Many children exhibited free cortisol of less than 2 µg/dL and 0.8 µg/dL, but did not demonstrate clinical evidence of critical illness-related cortisol insufficiency. The study ascertained that real-time free cortisol quantification, for the determination of adrenal function, is feasible to potentially help guide clinical decision making for cortisol replacement therapy in the pediatric intensive care unit. The study was published in September 2011, in Pediatric Critical Care Medicine.

Related Links:
Eunice Kennedy Shriver National Institute of Child Health
Ortho Clinical Diagnostics
Thermo Fisher Scientific