MON-487 Can a Single 60-Minute Cortisol Measurement Replace the Traditional ACTH Stimulation Test? A Study of Diagnostic Agreement

Abstract Disclosure: T. John: None. S. Teja Sathi: None. C. Casipit: None. N. Blocher: None. Background: The ACTH stimulation test is commonly used to evaluate for adrenal insufficiency (AI). Historically, a standard high-dose ACTH stimulation test included blood draws at 0, 30, 60, and occasionally 90 minutes. The test has been criticized for being time-consuming and resource-intensive, yet whether all of these time points for testing are necessary remains controversial. Recently, newer, more specific monoclonal antibody immunoassays for cortisol have widely replaced older, polyclonal antibody-based assays. To avoid overdiagnosis of AI, it is now recommended to replace the previous 18.0 mg/dL threshold with 14.0 - 15.0 mg/dL depending on the assay used. These newer assays may allow the potential for more efficient testing. Objective: To determine the diagnostic agreement of a single cortisol value at 60 minutes post-ACTH administration compared to a traditional ACTH stimulation test (with cortisol measurements at baseline, 30 minutes, 60 minutes, and 90 minutes) when using a monoclonal antibody assay. Method: We present a retrospective cross-sectional single-center analysis of results from all inpatient adult ACTH stimulation tests performed between February 2021 and July 2023. Cortisol was determined utilizing the Abbott Alinity monoclonal antibody-based chemiluminescent immunoassay, for which a cut-off of 14.6 mg/dL has been recommended to rule out AI. Primary outcomes are positive percent agreement (PPA) and negative percent agreement (NPA) of the 60-minute cortisol value alone compared to the traditional test. Secondary outcomes are PPA and NPA at 30 and 90 minutes. Results: A total of 215 stimulation tests were performed during the described time period. 52 tests were excluded for being incorrectly or incompletely performed. When comparing the 60-minute cortisol level to the traditional test, PPA was 100%, and NPA was 99.3%, with only 1 excess patient being diagnosed with AI when considering the 60-minute value alone. Cohen's Kappa was 0.972, indicating near perfect agreement. For the 30-minute value, the PPA was 100%, but the NPA was only 75.9%, indicating that this time point would result in overdiagnosis of AI. The 90-minute value resulted in both a PPA and NPA of 100%.· Conclusions: This study suggests that, especially with the advent of monoclonal antibody-based chemiluminescent immunoassays, using a single cortisol value at 60 or 90 minutes post-ACTH stimulation is a reliable method for diagnosing or ruling out AI. This efficient alternative to the traditional four-sample ACTH stimulation test offers the potential for cost and resource savings along with improved patient experience without sacrificing testing accuracy. Presentation: Monday, July 14, 2025