Simple method for estimating low muscle mass in persons with bioelectrical impedance analysis measurement difficulties.

Bioelectrical impedance analysis cannot be used to measure muscle mass in some individuals. We aimed to determine cutoff values for low skeletal muscle mass index in sarcopenia diagnosis, based on the fat-free muscle mass index estimated using body fat percentage prediction equations, without relying on bioelectrical impedance analysis. The study included 564 residents from Wakasa, Fukui Prefecture, with a mean age of 76.0 ± 7.1 years. Body composition assessments using bioelectrical impedance analysis were conducted. Three prediction equations for body fat percentage (Ito et al., Deurenberg et al., and Gallagher et al.'s model for Asians) were applied. The cutoff value of the fat-free muscle mass index corresponding to low skeletal muscle mass index in sarcopenia diagnostic criteria was determined using receiver operating characteristic curves. Receiver operating characteristic curve analysis showed that the formula by Ito et al. yielded the highest area under the curve for estimating low skeletal muscle mass index in men, at 0.83. In women, the formulas by Ito et al. and Gallagher et al. performed similarly, each achieving an area under the curve of 0.779. The fat-free muscle mass index estimated using the body fat prediction formulas appear to be useful for screening low skeletal muscle mass index.