A comparison of peak serum cortisol at 30 and 60 minutes after 1 µg adrenocorticotropic hormone stimulation in healthy Nigerian adults

Abstract

Background: Accurate diagnosis of adrenal insufficiency (AI) depends on the adrenocorticotropic hormone (ACTH) stimulation test, with the low-dose short Synacthen test (LDSST) increasingly used to assess adrenal function. Establishing precise reference values and identifying the optimal timing for peak cortisol measurement are essential, particularly across diverse populations. This study aimed to determine the peak serum cortisol response following 1 μg ACTH stimulation in healthy Nigerian adults.

Materials and Methods: We conducted a cross-sectional analysis of the healthy control arm of a larger study in northeastern Nigeria. Adults aged ≥18 years who were human immunodeficiency virus-negative and clinically healthy were enrolled in this study. A total of 132 subjects completed the LDSST, and data from 91 participants with unequivocal responses were analysed. Serum cortisol was measured at baseline (0 minutes), 30 minutes and 60 minutes post-stimulation using an enzyme-linked immunosorbent assay. Descriptive statistics were applied, with significance set at a P value of <0.05.

Results: The mean age of participants was 31.9 ± 11.2 years; 54.5% were male. Median basal cortisol was 310.6 nmol/L (interquartile range [IQR]: 258.5–393.1). Maximal stimulation occurred at 30 minutes, with a median cortisol of 605.0 nmol/L (IQR: 531.6–683.6), significantly higher than the 60-minute value of 498.5 nmol/L (IQR: 467.9–541.0). The third percentile cut-off for peak cortisol was 504.2 nmol/L at 30 minutes and 373.3 nmol/L at 60 minutes.

Conclusion: In this cohort, peak cortisol response occurred predominantly at 30 minutes post-ACTH. These findings support the use of 30-minute sampling to optimise LDSST sensitivity and highlight the importance of population-specific reference values for accurate diagnosis of AI.