Finger-Ring Test and Low Muscle Mass in Older Adults with Chronic Kidney Disease: A Cross-Sectional Study

Background and Objectives: Sarcopenia is highly prevalent among older adults with chronic kidney disease (CKD) and is associated with adverse clinical outcomes. The finger-ring (Yubi-wakka) test is a simple anthropometric screening tool based on calf circumference; however, its performance in older adults with CKD remains unclear. This study aimed to investigate the association of the finger-ring test with low muscle mass, sarcopenia, and comprehensive geriatric assessment parameters and to evaluate its diagnostic performance for identifying low muscle mass in older adults with CKD. Materials and Methods: This cross-sectional study included 115 patients aged ≥65 years with CKD who were evaluated in geriatric and nephrology inpatient services. After excluding two participants with missing finger-ring measurements, 113 individuals were analyzed. Muscle mass was assessed using bioelectrical impedance analysis and low muscle mass was defined according to EWGSOP2-based Turkish cut-off values. Demographic characteristics, anthropometric measurements, laboratory findings, and comprehensive geriatric assessment parameters were recorded. Correlation analyses, logistic regression models, receiver operating characteristic (ROC) analyses, and likelihood-ratio tests were performed. Results: Among 113 participants, 62 were classified as finger-ring positive (FR = 0) and 51 as finger-ring negative (FR = 1). Low muscle mass was significantly more frequent in the FR = 0 group than in the FR = 1 group (51.6% vs. 24.0%, p = 0.005). Finger-ring test results showed strong correlations with calf circumference (rho = 0.689, p < 0.001) and body mass index (BMI) (rho = 0.631, p < 0.001), whereas the correlation with muscle mass was modest (rho = 0.250, p = 0.008). For detecting low muscle mass, the finger-ring test demonstrated an area under the curve (AUC) of 0.643 (95% CI 0.554-0.732), sensitivity of 72.7%, specificity of 55.9%, positive predictive value of 51.6%, and negative predictive value of 76.0%. In multivariable analyses, BMI remained the strongest independent determinant of finger-ring test results, whereas the association with muscle mass lost statistical significance after BMI adjustment. Adding age and sex significantly improved discrimination, while the contribution of nutritional status was limited. Conclusions: The finger-ring test is associated with low muscle mass in older adults with CKD; however, its diagnostic performance is modest and appears to be substantially influenced by body size and calf circumference. Therefore, the finger-ring test should be considered a simple adjunctive screening tool rather than a stand-alone method for identifying low muscle mass in this population.