The short synacthen test (SST) is a widely used dynamic test for assessing primary adrenal insufficiency (AI) and non-classical adrenal hyperplasia. A morning cortisol test can be performed as a preliminary test to rule out adrenal insufficiency and it is a reliable predictor of SST outcome.[1],[2],[3],[4] If cortisol levels are low, a paired ACTH test help differentiate between primary and secondary AI. This approach helps avoid unnecessary dynamic tests, reduces healthcare costs, and minimizes the risks associated with SST and ITT. An Oxford retrospective study demonstrated a cortisol level of 343 nmol/L could predict a 'pass' on the SST with 100% specificity, regardless of the type of AI. [1] However, a morning cortisol level of 415 nmol/L is necessary to predict a normal insulin tolerance test, highlighting that patients with normal SST results can still have abnormal ITT results.[2] The clinical context remains crucial, especially in cases with normal or low ACTH levels, as a normal SST does not necessarily indicate a normal HPA axis, central causes of hypoadrenalism might still be undiagnosed.
In 2019, a retrospective audit conducted at Gold Coast University Hospital (GCUH) demonstrated an over-reliance on the SST as the preliminary test and many could have been avoided. The aim of this subsequent 2023 audit is to evaluate the influence of the prior audit on the hospital's practices and identify how many SSTs could have been avoided with morning cortisol alone.