April - June 2025, Volume 21, Issue 2

Erdem M, Aydin C, Helvaci B, Faki S, Baser H, Topaloglu O, Cakir B

Basal Morning Cortisol in Patients Referred for ACTH Stimulation Testing: Diagnostic Performance in a Retrospective Cohort

Acta Endo (Buc) 2025, 21 (2): 180-184
doi: 10.4183/aeb.2025.180

Context. Accurate diagnosis of adrenal insufficiency (AI) is crucial to prevent potentially lifethreatening complications. Early-morning basal serum cortisol is widely used to guide further testing, its diagnostic performance varies across clinical settings. Objective. To evaluate the diagnostic performance of early-morning basal cortisol in patients referred for ACTH stimulation testing and to determine whether basal cortisol alone can reliably exclude AI. Design and Methods. This retrospective cohort study included 404 adult outpatients (mean age 45.3 years; 18.8% male) who underwent standard-dose ACTH (250 μg) stimulation testing between 2018 and 2022. All consecutive patients with available early-morning basal cortisol measurements were included. AI was defined as a peak cortisol response <18 μg/dL (≈497 nmol/L). Diagnostic performance was assessed using logistic regression and receiver operating characteristic (ROC) analyses. Results. AI was diagnosed in 27 patients (6.7%). Basal cortisol levels were inversely associated with ACTH test failure and demonstrated moderate discriminatory ability (AUC = 0.85). Despite higher basal cortisol being associated with lower AI probability, a small proportion of patients within clinically relevant cortisol ranges still failed stimulation testing. Conclusion. Early-morning basal cortisol provides valuable diagnostic information but cannot reliably exclude adrenal insufficiency when used alone. Confirmatory dynamic testing remains necessary to ensure diagnostic safety.

Keywords: adrenal insufficiency, basal cortisol, ACTH stimulation test, diagnostic accuracy, predictive values.

Correspondence: Mehdi Erdem, M.D., Department of Endocrinology and Metabolism, Sincan Training and Research Hospital, Cankaya, Ankara, Turkey, E-mail: drmehdihoussein@gmail.com