Blood Urea Nitrogen/Creatinine Ratio in Cushing's Syndrome: Associations With Disease Status and Postoperative...

Although various tests are used for Cushing's syndrome (CS) screening and diagnosis, none exhibit ideal sensitivity or specificity. This study evaluates the association of the blood urea nitrogen (BUN)/creatinine ratio with disease status in CS and subclinical Cushing's syndrome (SCS), and with postoperative changes in patients with CS.

A single-center, observational, cross-sectional study conducted at Endocrinology and Metabolic Diseases Clinic of a tertiary training and research hospital in Istanbul, Turkey (2017-2022).

This study included 229 individuals: 151 CS/SCS patients and 78 healthy controls. CS cases were classified as adrenocorticotropic hormone (ACTH)-dependent (n = 52) or ACTH-independent (n = 34).

BUN/creatinine ratios were compared among CS, SCS, and control groups, as well as between pre- and posttreatment states in CS patients. Correlations between BUN/creatinine ratio and standard CS diagnostic tests were analyzed. Receiver operating characteristic (ROC) analysis was performed to evaluate the discriminatory performance of the BUN/creatinine ratio between CS and control groups.

BUN/creatinine ratios were significantly higher in CS, ACTH-independent CS, and SCS groups compared to controls. Cutoff values were > 15.34 for CS, > 13.67 for ACTH-independent CS, and > 19.8 for SCS. The BUN/creatinine ratio correlated positively with basal plasma cortisol, 1 mg dexamethasone suppression test (DST), and midnight serum cortisol in ACTH-dependent CS (p = 0.047, 0.038, 0.004). In all CS patients, it correlated with 1-mg DST and midnight serum cortisol (p = 0.041, 0.049). In ACTH-dependent CS, a positive correlation was found between pituitary adenoma diameter and the preoperative BUN/creatinine ratio (p = 0.036).

The BUN/creatinine ratio may provide supportive information associated with CS status and postoperative changes in patients with CS, particularly when standard tests are unavailable or inconclusive. Larger multicenter studies are needed to confirm its clinical utility.