Background/Objectives: Distinguishing glomerulonephritis (GN) from diabetic kidney disease (DKD) and nephrosclerosis (NS) is clinically important. Urinary uromodulin (uUMOD), a biomarker of renal tubular integrity, may help discriminate among these chronic kidney disease (CKD) etiologies. We evaluated the diagnostic utility of uUMOD for differentiating GN from DKD and NS. Methods: This retrospective single-center study included 90 patients with biopsy-proven GN (n = 30), DKD (n = 25), or NS (n = 35). First-morning spot urine samples obtained before biopsy were analyzed for uUMOD concentration and normalized to urinary creatinine levels (uUMOD/Cr). Results: The uUMOD/Cr ratio was significantly higher in GN (21.2 mg/gCr [10.3–31.3]) than in DKD (5.5 [3.6–12.3], p < 0.001) or NS (10.7 [6.4–19.9], p = 0.021). In multivariate analyses adjusted for age, sex, estimated glomerular filtration rate, interstitial fibrosis, and urinary protein, the uUMOD/Cr ratio was independently associated with GN (p = 0.003) and this correlation remained statistically significant after additional adjustment for diabetes mellitus. Receiver operating characteristic curve analysis showed an area under the curve value of 0.833 for GN versus DKD, 0.714 for GN versus NS, and 0.764 for GN versus DKD and NS combined. A cutoff value of 16.5 mg/gCr yielded 72.8% sensitivity and 70.0% specificity for identifying GN. Conclusions: uUMOD secretion is preserved in GN compared to DKD or NS and shows moderate diagnostic utility for differentiating between these biopsy-proven CKD etiologies. uUMOD may serve as a simple, noninvasive biomarker when biopsy is difficult or clinical findings are inconclusive.

Background/Objectives: Accurate assessment of the glomerular filtration rate (GFR) is essential for managing chronic kidney disease (CKD). Although creatinine-based estimated GFR (eGFRcr) may be affected by reduced muscle mass, the contribution of muscle characteristics beyond muscle mass remains unclear. This study investigated whether phase angle (PhA), a bioelectrical impedance analysis-derived indicator associated with muscle quality, provides complementary information beyond appendicular skeletal muscle mass (ASM) regarding discordance between eGFRcr and a creatinine clearance (CCr)-based reference estimate. Methods: We enrolled 86 adults with CKD not receiving maintenance dialysis. CCr was calculated from 24 h urine collections, indexed to a standard body surface area (BSA) of 1.73 m², and multiplied by 0.715. KOI was calculated as eGFRcr divided by (BSA-indexed CCr × 0.715). A KOI > 1.2 was used as an exploratory threshold for clinically significant discordance. Results: KOI > 1.2 was observed in 24.4% of patients. KOI was negatively correlated with ASM (r = −0.301, p = 0.005) and PhA (r = −0.451, p < 0.001). Adding PhA to a multivariable linear regression model including ASM improved model performance (adjusted R², 0.060–0.200). Multivariable logistic regression, including ASM and PhA as explanatory variables, showed that only PhA remained independently associated with KOI > 1.2 (odds ratio, 0.258; 95% CI, 0.113–0.585; p = 0.001). Conclusions: PhA may provide complementary information beyond skeletal muscle mass for identifying patients with greater discordance between eGFRcr and corrected, BSA-indexed CCr. Further studies using measured GFR are needed to validate these findings.