Endocrine Abstracts

Introduction: The specificity of cortisol after 1 mg dexamethasone (cortisol_DST) ≥50 nmol/l as a criterion for mild autonomous cortisol secretion (MACS) is approximately 80% in patients with adrenal incidentalomas (AI). The aim was to study the associations of cortisol_DSTto age, BMI, and renal function. We used machine learning models to uncover potential non-linear associations.

Methods: We studied 1129 patients with AI examined from 2005 to 2015 at Skåne University Hospital and Helsingborg Hospital. Cortisol_DSTwas ln-transformed in the analyses. The covariates studied were gender, age, BMI, eGFR, treatment with inhalation steroids, size of the AI, and size of the smallest AI in patients with bilateral AI (set to 0 in unilateral AI). Various machine learning models were trained to fit the data and examined using feature importance analysis and partial dependence plots. Partial dependence plots show the marginal effect on cortisol_DSTof a covariate averaging over other covariates.

Results: Cortisol_DST was strongly associated to the size of the AI but had weaker associations to age, BMI, and eGFR according to permutation importance. The partial dependence plots indicated relatively linear relationships for cortisol_DSTto age (positively) and eGFR (negatively). There was a negative relationship to BMI at levels below 30 kg/m². Using linear regression, we found that cortisol_DST increased 10% (95% CI, 7–14%) for each 10-year increase in age. In patients with BMI below 30 kg/m², cortisol_DSTdecreased 19% (95% CI, 14–23%) for each 5 kg/m² increase in BMI. We found no association at BMI levels above 30 kg/m². Cortisol_DST increased 9% (95% CI, 6–11%) for each 10 ml/min/1.73m² decrease in eGFR.

Conclusions: Cortisol_DST is positively associated to age, negatively to BMI if below 30 kg/m², and negatively to eGFR. These associations should be considered before diagnosing MACS.