Abstract
Background This study aims to investigate the relationship between suppressed cortisol levels measured after the 1-mg dexamethasone suppression test (DST) and age based on the hypothesis that aging can alter the activity of the hypothalamic-pituitary-adrenal (HPA) axis. Methodology Data obtained by the retrospective evaluation of suppressed 1-mg overnight DST results of adults aged ≥18 years with adrenal incidentaloma or suspected endogenous hypercortisolemia between December 2021 and March 2023 were subjected to age-dependent correlation analysis. Individuals aged between 18 and 90 years (n = 1111) were classified into the following four groups: <30 years, 30-49 years, 50-69 years, and >70 years. DST results were compared according to age groups. Results Median post-DST cortisol was 18.49 nmol/L, with a level of 17.9 nmol/L in females and 20.7 nmol/L in males. The overall rate of DST suppression was 62.7%, with a rate of 63.8% in females and 59.7% in males. On pairwise comparisons of all age groups, there was a difference in post-DST cortisol levels (p = 0.000). Our statistical analysis revealed a strong positive correlation between age and cortisol levels after DST. Conclusions The negative feedback mechanism for cortisol may be altered in older patients. Therefore, the 1-mg DST may yield a higher rate of false positives in the elderly.