Investigating the Clinical Appropriateness of Short Synacthen Testing and Utility of Pretest Cortisol to Predict Short Synacthen Testing Outcomes: A Tertiary Center Experience in Southeast Asia.

Objective: No studies have investigated the predictors of an adequate cortisol response to the short synacthen test (SST) and the appropriateness of patient selection for SST in the Southeast Asian population. The aim of our study is to investigate the predictors and indications of SSTs and concondance of SSTs conducted with outcomes.

Methods: This is a retrospective study investigating all SSTs performed over a year in a tertiary center. Clinical data of patients with SSTs between February 2022 and February 2023 were extracted. We determined the appropriateness of SST testing. Binary logistic regression was used to assess the parameters that predict adequate cortisol response on SST. The proportion of individuals with biochemical "pass" or "fail" on SST was compared with the Χ² test. Baseline cortisol levels that predicted SST pass were determined using area under receiving operating characteristics curves.

Results: Of the 781 SSTs, 83.9% of SSTs showed an adequate cortisol response. Postural hypotension (26.9%) and exogenous glucocorticoid administration (14.2%) were common indications for SST. In our cohort, 50.2% of the SSTs were inappropriately indicated. Pretest serum cortisol and albumin predict biochemical pass on SST. A pretest cortisol level of 300 nmol/L predicted SST response with 93% sensitivity and a cortisol level of <100 nmol/L confirmed adrenal insufficiency (AI) with 97.3% specificity. Using these cortisol thresholds could avoid 302 (38.5%) of SSTs.

Conclusion: Our analysis showed that clinical features of AI do not reliably predict SST outcomes. We advocate careful assessment of the pretest probability of AI in patients referred for SST. A pretest cortisol level can reduce the number of SSTs, with cost savings implications.