Baseline morning cortisol level as a predictor of pituitary-adrenal reserve: A comparison across three assays

Abstract

Context

The short ACTH stimulation test (250μg) is the dynamic test most frequently used to assess adrenal function. It is possible that a single basal cortisol could be used to predict the dynamic response, but research has been hampered by the use of different assays and thresholds.

Objective

To propose a morning baseline cortisol criterion of three of the most commonly-used modern cortisol immunoassays - Advia Centaur (Siemens), Architect (Abbott) and the Roche Modular System (Roche) - that could predict adrenal sufficiency.

Design

Observational, retrospective cross-sectional study at two centres.

Patients and Measurements

Retrospective analysis of the results of 1019 SSTs with the Advia Centaur, 449 SSTs with the Architect, and 2050 SSTs with the Roche Modular System assay. Serum cortisol levels were measured prior to injection of 250μg Synacthen and after 30 minutes. Overall, we were able to collate data from a total of 3518 SSTs in 3571 patients.

Results

Using receiver-operator curve analysis, baseline cortisol levels for predicting passing the SST with 100% specificity were 358 nmol/l for Siemens, 336 nmol/l for Abbott and 506 nmol/l for Roche. Utilising these criteria: 589, 158 and 578 SSTs respectively for Siemens, Abbott and Roche immunoassays could have been avoided.

Conclusions

We have defined assay-specific morning cortisol levels that are able to predict the integrity of the hypothalamo-pituitary-adrenal axis. We propose that this represents a valid tool for the initial assessment of adrenal function and has the potential to obviate the need for dynamic testing in a significant number of patients.

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