Endocrine Abstracts

Context: A low screening morning serum cortisol is used to select patients for ACTH stimulation testing (SST) to diagnose adrenal insufficiency (AI) but may be affected by pre-analytical factors. Careful preparation to hold potentially confounding medications beforehand may yield more reliable screening results and preclude the need for subsequent stimulation testing.

Objective: To compare the ability of a morning serum cortisol (ordered by clinicians in the real world setting) to an optimally collected basal zero-minute cortisol at the time of SST (after holding confounding medications) to predict the presence of AI with 100% sensitivity.

Methods: Retrospective chart review of 835 patients with ACTH stimulation testing from a tertiary endocrine testing clinic. Linear regression to compare Roche Cortisol II immunoassay screening cortisol vs optimally collected cortisol measurements after holding confounding medications. Receiver operating characteristic (ROC) curve analyses to identify 100% sensitivity threshold for AI.

Results: The majority of patients passed the SST (n = 756, 90.5%). There was a poor correlation between screening morning cortisol and optimally collected cortisol measurements, r = 0.34 (95% CI, 0.25-0.42). Real world screening morning cortisol measurements had moderate discrimination for the diagnosis of AI (AUC 0.80; 95% CI, 0.77-0.82; P < 0.001). A real world screening cortisol threshold of 262 nmol/l had 100% sensitivity for AI but only 15% specificity. Applying this threshold would save 112 (13.4%) SSTs. In contrast, an optimally collected cortisol had strong discrimination for AI (AUC 0.89; 95% CI, 0.87 – 0.91; P < 0.0001). A threshold of 245 nmol/l had 100% sensitivity and 43% specificity for the diagnosis. Applying this threshold would save 151(18.1%) tests.

Conclusion: A screening cortisol measured after careful attention to pre-test patient preparation variables may make a significant number of ACTH stimulation tests unnecessary without missing any cases of adrenal insufficiency.