A Pragmatic Approach to Monitor for Adrenal Axis Recovery After a Failed Short Synacthen Test

To identify a morning cortisol threshold value which confirms non-recovery of the adrenal axis and therefore negates the need for a short Synacthen test (SST) in those with known adrenal axis insufficiency.

We collected data from all SSTs (n = 1570 tests; n = 952 individuals) conducted in our hospital over a 10-year period spanning between 1st February, 2013, and 30th January, 2023. We included all tests where baseline cortisol levels were taken before 9:30 am Both 30- and 60-minute cortisol values were measured. Cortisol was measured using the Abbott Architect method. We used the full SST dataset to construct a quantile regression model to predict the 95% centile of peak cortisol response. This model was refitted to the SST follow-up data for those who failed a first SST (n = 115 tests; n = 66 individuals) to identify the baseline cortisol value below which there was a less than 5% chance of passing an SST.

Those with an early morning cortisol of ≤126 nmol/L had ≥95% chance of failing an SST. Sixty percent of follow-up SSTs (69/115) exhibited baseline cortisol values below this threshold, and none of these passed an SST.

An early morning cortisol ≤126 nmol/L is common in those followed for adrenal axis recovery and is an accurate indicator of non-recovery. 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. Using this approach could considerably reduce the need for follow up SSTs in this patient cohort.