Serum morning cortisol as a screening test for adrenal insufficiency

Abstract

Objective: To evaluate the performance of morning serum cortisol (MSC) compared to a 10 mg adrenocorticotropic hormone (ACTH) stimulation test in the diagnosis of adrenal insufficiency (AI). Methods: A retrospective, cross-sectional analysis of ACTH stimulation tests were conducted. From a total of 312 potentially eligible ACTH stimulation tests, 306 met the inclusion criteria. The population was randomized into 2 groups: test (n = 159) and validation (n = 147). In the test group, the receiver operating characteristics curve test evaluated the diagnostic performance of MSC. Results: A subnormal cortisol response to ACTH was found in 25.8% of the test group. The area under the curve values of MSC to predict AI at +30 minutes, +60 minutes, or at maximal cortisol response were 0.874, 0.897, and 0.925 (95% confidence interval [CI] 0.81 to 0.92, 0.83 to 0.93, and 0.87 to 0.96). The Youden index was 234.2 mmol/L with a sensitivity of 83.3% (95% CI 65.2 to 94.3%), and a specificity of 89.1% (95% CI 82.4 to 93.9%). Positive and negative predictive values were 64.1% (95% CI 47.1 to 78.8%) and 95.8% (95% CI 90.5 to 98.6%). There was no difference in age, gender, AI prevalence, or mean serum cortisol at +30 or +60 minutes in the validation group; however, a lower mean MSC value was found. Lower sensitivity and specificity values (88.3% and 60%, respectively) were found for the 234.2 mmol/L cutoff value. Conclusion: This study supports the role of MSC as a first-step diagnostic test in patients with clinically suspected AI. The short stimulation test could be omitted in almost half of the cases. Prospective and longitudinal studies to reproduce and confirm the cutoff values proposed are warranted.