A Practical Anthropometric Model Incorporating Calf Circumference to Estimate Appendicular Lean Mass in Women with...

Accurate assessment of appendicular lean mass (ALM), an essential component for evaluating sarcopenia and nutritional status, typically requires dual-energy X-ray absorptiometry (DXA); however, its widespread clinical application is limited by cost and accessibility. This study aimed to develop a simple anthropometry-based equation for estimating ALM in women with systemic lupus erythematosus (SLE) and to compare its predictive performance with existing models. This cross-sectional study included 92 female patients with SLE. A multiple regression model was developed, incorporating height, body weight, calf circumference (CC), and age. Model performance was internally validated using five-fold cross-validation, and agreement with DXA-measured ALM was assessed using out-of-fold predictions. The diagnostic performance for detecting low skeletal muscle mass index (SMI) was also evaluated and compared with previously published equations (Hwang and Santos). The predicted ALM showed good correlation with measured ALM (R² = 0.76) and moderate agreement (Lin's concordance correlation coefficient [CCC] = 0.829), with a root mean square error of 1.38 kg. Sensitivity and specificity for detecting low SMI were 65.0% and 88.9%, respectively. The proposed equation demonstrated comparable or superior performance (CCC: Hwang 0.782; Santos 0.672) and may serve as a practical tool for estimating ALM in female patients with SLE.