Endocrine Abstracts

Background: The short Synacthen test (SST) is commonly used for assessing adrenal reserve. Depending on the cause, we often use serial SSTs in current practice, to assess whether people with adrenal insufficiency (AI) have adrenal axis recovery. We aimed to explore if baseline cortisol levels were a suitable screening test for recovery in people with AI rather than using serial SST in all cases.

Methods: We retrospectively reviewed all SSTs (n=1,570 tests; n=952 individuals) conducted in our hospital over a 10-year period (1st February 2013 to 30th January 2023) that had a baseline cortisol taken before 9:30 am. We measure both 30- and 60-minute cortisol values for all SSTs and currently use the Abbott Architect method. We used the follow-up SSTs (n=115 tests; n=66 individuals) for those who failed their first SST to see whether baseline cortisol could be used to predict a threshold below which there was a less than 5% chance of passing an SST. We used the full SST dataset to refine the construction of a quantile regression model to predict the 95% centile of peak cortisol response. This model was refitted to the SST data for those who failed the first SST.

Results: Individuals with a baseline cortisol of ≤126 nmol/l, had a 95% chance of failing an SST. Of all our follow-up SSTs, 60% (69 of 115) had a baseline cortisol of ≤126 nmol/l; none of these passed an SST.

Conclusions: A baseline 9 am cortisol ≤126 nmol/l is common in those followed for AI recovery and is an excellent indicator of non-recovery of adrenal axis. Baseline cortisol measurements are therefore a simple way of screening for adrenal axis recovery. Those with a cortisol of >126 nmol/l should go on to have an SST.