7560 Using a Single Pre-test Cortisol Level To Reduce The Need For Dynamic Testing For Adrenal Insufficiency In A Southeast Asian Population

Abstract Disclosure: V. Ramadoss: None. L. Tan: None. A.E. Teo: None. K. Lazarus: None. K. Meeran: None. D. Deepak: None. L. Ong: None. C. Khoo: None. P. Eng: None. Introduction: The Short Synacthen Test (SST) is widely used in clinical practice to assess Adrenal Insufficiency (AI). Despite its relative ease of administration, Synacthen use is limited by its availability and its administration demands supervision by experienced staff, resulting in increased testing cost. A single measurement of serum cortisol has been shown to predict AI, but the suggested threshold varies according to the patient cohort studied, assay variation and the prevalence of the condition relative to the size of population tested. This study aims to (a) identify a threshold cortisol level to screen for AI in a South-East Asian population and (b) to determine the utility of a stimulated 60-minute cortisol level in the diagnosis of AI. Methods: This is a retrospective analysis of SSTs (250 micrograms) performed in our institution between 28th February 2022 to 28th February 2023. Serum cortisol in our institution was measured by Abbott Alinity analysers. We defined a normal response as a stimulated cortisol value of ≥ 420nmol/L at either 30-minutes, 60-minutes, or at both time points. Logistic regression analysis was performed to predict normal responses based on baseline cortisol level. Results: Median cortisol level at baseline, 30-minutes, and 60-minutes after Synacthen stimulation were 254 (IQR 191-320) nmol/L, 499 (IQR 415 -585) nmol/L, 574 (IQR 476 -662) nmol/L respectively. A total of 785 SSTs were performed, out of which 83.1% were normal and 16.9% were abnormal. Of the 785 SSTs, 55 (7.0%) would have failed if only the 30-minute cortisol was assessed without the 60-minute value, whereas 10 (1.4%) would have failed if only the 60-minute cortisol was assessed without the 30-minutes value. An early morning basal cortisol (0800am to 1200pm) cut-off of <300nmol/L identified subnormal cortisol with 95.0% sensitivity and an afternoon cortisol (1200pm to 1700) of < 312nmol/L achieved 95.2% sensitivity. A basal cortisol level of < 100nmol/L will confirm AI with 97.3% specificity. Using a basal cortisol level of ≥ 300nmol/L, 94.8% of individuals go on to pass the SST. Use of this basal cortisol value would avoid 252 (32.1%) SSTs. Conclusion: A single measurement of basal cortisol of ≥ 300nmol/L has the potential to exclude AI with 95% sensitivity on Abbott Alinity platform in our cohort of patients. Using a threshold cortisol level of 300nmol/L, at least 32% of the SSTs could be avoided. This would have improved patients experience with cost savings implications. Furthermore, a stimulated 60-minute cortisol level identifies 55 (7%) of individuals who would otherwise be misclassified as AI, thereby avoiding unnecessary long-term glucocorticoid replacement. Presentation: 6/1/2024