Multicenter performance evaluation of a second generation cortisol assay.

BACKGROUND

Untreated disorders of the adrenocortical system, such as Cushing's or Addison's disease, can be fatal, and accurate quantification of a patient's cortisol levels is vital for diagnosis. The objective of this study was to assess the analytical performance of a new fully-automated Elecsys® Cortisol II assay (second generation) to measure cortisol levels in serum and saliva.

METHODS

Four European investigational sites assessed the intermediate precision and reproducibility of the Cortisol II assay (Roche Diagnostics) under routine conditions. Method comparisons of the Cortisol II assay vs. liquid chromatography-tandem mass spectrometry (LC-MS/MS), the gold standard for cortisol measurement, were performed. Cortisol reference ranges from three US sites were determined using samples from self-reported healthy individuals.

RESULTS

The coefficients of variation (CVs) for repeatability, intermediate precision, and reproducibility for serum samples were ≤2.6%, ≤5.8%, and ≤9.5%, respectively, and for saliva were ≤4.4% and ≤10.9%, and ≤11.4%, respectively. Agreement between the Cortisol II assay and LC-MS/MS in serum samples was close, with a slope of 1.02 and an intercept of 4.473 nmol/L. Reference range samples were collected from healthy individuals (n=300) and serum morning cortisol concentrations (5-95th percentile) were 166.1-507 nmol/L and afternoon concentrations were 73.8-291 nmol/L. Morning, afternoon, and midnight saliva concentrations (95th percentile) were 20.3, 6.94, and 7.56 nmol/L, respectively.

CONCLUSIONS

The Cortisol II assay had good precision over the entire measuring range and had excellent agreement with LC-MS/MS. This test was found suitable for routine diagnostic application and will be valuable for the diagnosis of adrenocortical diseases.