Effect of albumin concentration on serum cortisol measured by the Bayer Advia Centaur assay

Introduction A poor comparison was seen between the Bayer Advia Centaur and the Roche Elecsys cortisol methods using samples sent to the laboratory for cortisol analysis. They were predominantly from patients attending the Endocrine outpatients clinic or patients in the intensive therapy unit. We investigated the effect of albumin concentration on the performance of both assays. Methods For the samples used in the patient comparison, the laboratory database was searched for any concomitant albumin concentrations (Beckman LX20 BCP method). A series of recovery experiments were performed combining samples with normal albumin and undetectable cortisol concentrations with samples with detectable cortisol but low albumin concentrations. Results Albumin concentration accounts for almost 50% of the variation in the difference between the two methods. The Bayer Advia Centaur method shows significant under-recovery at albumin concentrations lower than 24 g/L. Conclusion This under-recovery will significantly affect the diagnosis of adrenal insufficiency in critically ill patients with low albumin concentrations.