Endocrine Abstracts

Background: Adrenal insufficiency (AI) is a life-threatening condition which requires long term glucocorticoid (GC) replacement. Patient misdiagnosis results in inappropriate GC use, which has significant adverse effects and is associated with an increased mortality risk. The insulin tolerance test (ITT) is the gold standard test for diagnosis, but the widely accepted cut-off value of ≤550 nmol/l used to diagnose AI is founded on outdated immunoassays. Use of this cut-off in an era of more specific immunoassays therefore risks misdiagnosis and subsequent unnecessary GC exposure.

Methodology: This retrospective analysis assessed 297 ITT cortisol responses using the Abbott-Alinity analyser platform in patients with suspected AI over a period of approximately 12 years (August 2010-January 2022). Patients were classified as having AI or not, based on a comprehensive clinical review of electronic patient records from the point of test to the present day by a panel of adrenal specialists.

Results: Using the current institutional cut-off value of 500 nmol/l, receiver operating characteristic (ROC) analysis identified a 100.0% sensitivity and 43.4% specificity (area under the curve 0.9812). This gave a negative predictive value (NPV) of 100.0% and a positive predictive value (PPV) of 28.6%. Using a lower cortisol threshold value of 416 nmol/l on the Abbott analyser platform maintained a sensitivity of 100.0% and improved specificity to 87.2%, improving the PPV to 64.0%

Conclusion: This is the largest review of ITT data in AI patients to date. Data supports lowering the Abbott analyser ITT cortisol threshold to 416ce:hsp sp="0.25" />nmol/l. Use of this improved cut-off avoids unnecessary glucocorticoid replacement therapy in 106 (41.6%) individuals in this study.