Endocrine Abstracts

Background: Cut-offs for basal cortisol (early morning) have been determined to predict the 30-minute cortisol level post-synacthen, but not for determining when patients with suspected tertiary adrenal insufficiency (AI) are weaned off glucocorticoids.

Aims: The aim of this study was to compare the predictive values of basal cortisol, basal ACTH and basal cortisol:ACTH ratio to determine appropriate thresholds to reduce the required number of Short Synacthen tests (SST).

Methods: This was a retrospective cohort study of all adult patients on long-term glucocorticoids who were referred to a tertiary endocrinology steroid clinic for suspected tertiary AI between 2015-2022 and underwent an SST (08:00-12:00). Basal cortisol, basal ACTH and cortisol:ACTH cut-offs with 95% and 99% specificity and sensitivity were determined via receiver operating characteristic (ROC) curve analysis. AI was defined as post-synacthen 30-minute cortisol of <430 nmol/l, analysed using Roche Elecsys II (Roche, Mannheim, Germany) assay.

Results: A total of 262 patients underwent 443 SSTs, of which 36.3% tests were normal. The ROC curve analysis showed that basal cortisol was the best-performing test with area under curve of 0.89 (95%CI 0.85-0.92) compared to 0.56 (95%CI 0.51-0.62) and 0.80 (95%CI 0.76-0.84) for basal ACTH and cortisol:ACTH, respectively. Basal cortisol cut-offs with 95% and 99% specificity to predict adrenal sufficiency were 285 and 349 nmol/l respectively. Analysis of patients with basal cortisol between these two cut-offs showed that none had an AI-related admissions in the following 12 months. These 57 patients consisted of 54 who were successfully weaned while observing standard steroids sick-day rules, two remained on glucocorticoids long-term, and one was weaned later.

Conclusion: Basal cortisol is superior to the basal ACTH and cortisol:ACTH in predicting SST outcome and the 95% specificity threshold of 285 nmol/l can be used to wean patients off glucocorticoids.