Abstract / Summary
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.