9360 Evaluating The More Accurate Indicator Of Kidney Function In Mild Autonomous Cortisol Secretion: EGFR Creatinine Versus EGFR Cystatin

Abstract Disclosure: L. Rahimi: None. J. Saini: None. E. Atkinson: None. S. Achenbach: None. A. Kattah: None. I. Bancos: None. Introduction: Patients with mild autonomous cortisol secretion (MACS) have higher prevalence of cardiovascular comorbidities including chronic kidney disease. However, considering that patients with MACS may have relative skeletal muscle atrophy, it is unclear whether the creatine-based assessment of kidney function is accurate in this population. Objective: To characterize the differences in assessing estimated glomerular filtration rate using cystatin (eGFRcys) versus creatinine (eGFRcre) in patients with MACS versus referent subjects. Methods: Cross-sectional single-center study, 2019-2022. MACS was defined as serum cortisol concentration >1.8 mcg/dL after the 1 mg overnight dexamethasone suppression test (DST). For each patient, eGFRcre, eGFRcys and eGFRcre/eGFRcys ratio were measured and compared between the two groups. Body composition was measured by DXA scan. The Kruskal-Wallis test was used to compare measurements between groups. Result: A total of 37 patients with MACS (median age 59 years (interquartile range, IQR 47-67), 25 (68%) women) and 45 referent subjects (median age 57 years (IQR 51-66), 30 (67%) women) were included. The distribution of BMI, total body fat mass and total body lean mass were similar between the two groups. In the MACS cohort, the median cortisol following 1-mg DST was 3.0 ug/dL (IQR, 2.2-4.0). While assessment of kidney function with eGFRcre showed no differences between patients with MACS and referent subjects (median 85.1 vs 87.0 ml/min/1.73m2, P=0.431), kidney function using eGFRcys was lower in MACS (median 78.0 vs 89.3 ml/min/1.73m2 in referents, P<0.014), resulting also in a higher eGFRcre/eGFRcys ratio (median 1.07 vs 0.97 in MACS vs referents, P=0.053). After adjusting for age, sex, and BMI, a higher 1 mg DST cortisol level in the MACS cohort was associated with a higher eGFRcre/eGFRcys ratio (Spearman correlation coefficient of 0.35, P = 0.042). Lower eGFRcys was associated with higher fat mass (Spearman correlation of -0.26, P = 0.023), and a higher eGFRcre/eGFRcys ratio showed a trend towards lower lean mass (Spearman correlation of -0.20, P = 0.081). Conclusion: Creatinine-based eGFR assessment in patients with MACS underestimates the degree of kidney dysfunction, likely due to underlying skeletal muscle atrophy. eGFRcys is a more accurate indicator of kidney function in patients with hypercortisolism. Presentation: 6/1/2024