Endocrine Abstracts

Introduction: The Short Synachten Test (SST) is the gold standard test for assessing adrenal insufficiency, however these can be time and resource consuming. Improved cortisol assays (Scottish consensus) currently advise a cut-off of 430 nmol/l at 30 minutes . However, there is no clarity about the optimum baseline cortisol level and recommendations range varies from 300–500 nmol/l.

The aim of this study was to establish a single baseline cortisol concentration cut-off which could reliably exclude adrenal insufficiency for this Scottish sub-population. We also assessed if both 30 minute and 60 minute SSTs have clinical necessity.

Method: 188 SSTs performed over a 1 year period (2016–2017), at the Victoria Hospital in Fife, were retrospectively analysed for indications, results (baseline, 30 and 60 minutes) and if on long term (LT) steroids. Receiver-operating characteristic (ROC) curve analysis was then performed to assess the optimalserum cortisol level and cut-off for the SSTs.

Results: Out of the 188 patients, 77% (n = 145) passed the SST at 30 minutes, 6% (11) passed only at 60 minutes and 17% (32) failed at both time cut-offs. A total of 47% (87) patients were on LT steroids. These accounted for 70% (22) that failed overall but represented 80% of those that required the 60 minute test to pass. ROC curve analysis identified a cut-off level of 350 nmol/l (94% specificity and 28% sensitivity) for 30 minute cortisol. This excluded 2 patients who failed the SST. A further cut-off level of 250 nmol/l increased specificity and sensitivity to 91% and 57% respectively, but excluded 3 patients that failed.

Discussion: This study showsthat only a 30 minute SST is required in most cases to identify adrenal insufficiency. This reduces the time and financial costs associated with SSTs. However, 60 minute SSTs should be considered in patients on LT steroids, acutely unwell or with a pituitary disorder. This study suggests that a novel cortisol cut-off level of 350 nmol/l at 30 minutes in a SST can be safely used to identifypatients with adrenal insufficiency in a Scottish population. It also suggests a novel morning baseline cortisol level of <250 nmol/l can be used to classify SST requirement. Limitations to this study include the small population sample, the large number on steroids and unknown timings of the SSTs. Further studies in a larger population size shall be performed to confirm these results.