Endocrine Abstracts

Background: The NICE guideline Adrenal insufficiency: identification and management [NG243] was published in August 2024. It states an 8-9 am cortisol concentration of >300 nmol/l suggests that adrenal insufficiency is very unlikely. Until now, we have made the same assertion only for random samples >430 nmol/l, which is the recommended cut-off for our assay post-Synacthen. Patients with 9 am cortisol <430 nmol/l may require a Synacthen test to demonstrate adequate adrenal reserve.

Aim: To assess local data and collect evidence for an assay and population specific concentration at which adrenal insufficiency is very unlikely.

Method: In line with other published studies, retrospective Synacthen test data was examined. Three years of data from Doncaster and Bassetlaw NHS FT was gathered, and Receiver Operated Characteristics (ROC) analysis performed to determine baseline cortisol concentrations that predict a pass outcome for a Synacthen test at 0.95 and 0.99 sensitivity. Data was assessed in three groups (a) all data, (b) baselines taken between 8-10 am and (c) baselines not taken between 8-10 am.

Results: 1231 SST data sets were analysed, of which 128 (10.4%) already had a baseline cortisol >430 nmol/l. Of the remaining 1103 patients, 205 (18.6%) did not have cortisol >430 nmol/l at 30 minutes post-Synacthen. ROC analysis suggested baseline results ranging from 306-372 nmol/l could predict a post-Synacthen cortisol of >430 nmol/l, depending on the data group and sensitivity chosen.

Conclusion: The concentration at which NICE states adrenal insufficiency is very unlikely is lower than all cut-offs modelled here. Not requiring a Synacthen test in patients with cortisol above 306-372 nmol/l could reduce the Synacthen test workload by 11.1-32.5%. Local guidance for primary care has been created between the Endocrine and Biochemistry departments to maximise efficiency and patient safety.