Muscle mass is used in diagnosing sarcopenia. Computed tomography (CT) scanning and magnetic resonance imaging (MRI) permit accurate differentiation of the bone, fat, and lean body tissue and are gold standards for muscle mass evaluation [
5]. However, these methods require large, expensive, and nonportable equipment, and therefore, there are limitations to their use in routine clinical practice. On the other hand, dual-energy X-ray absorptiometry (DXA) results in low radiation exposure among patients. The Health ABC study reported that participants were assessed using DXA and were classified as sarcopenic using two different approaches of adjusting lean mass to body size: appendicular lean mass divided by height squared and appendicular lean mass adjusted for height and body fat mass (residuals) [
41]. In addition, the cutoff values of skeletal muscle mass index by DXA (appendicular skeletal muscle mass index (kg)/body height (m)
2) were 7.23 kg/m
2 for men and 5.67 kg/m
2 for women. Unfortunately, DXA is also a nonportable equipment. Another method used is bioelectrical impedance analysis (BIA), which measures fat mass and lean body mass. Although the reliability of BIA is somewhat compromised in patients with a BMI of ≥ 35 kg/m
2, it is a relatively inexpensive and portable alternative to DXA for accurate evaluation of body composition [
42]. A working group in Asia reported diagnostic criteria for sarcopenia for Asians in 2015, and the cutoff values for muscle mass measured by BIA were reported [
43]. The cutoff values for BIA were 7.0 and 5.7 kg/m
2 for men and women, respectively. However, no standardized diagnostic criteria are available for sarcopenia, and results differ depending on the diagnostic criteria used.