Different Associations of Skeletal Muscle Mass Index and Creatinine-To-Cystatin C Ratio With Muscle Mass and Myosteatosis: The J-SHIPP Study

When assessing sarcopenia, physicians usually evaluate muscle mass by the skeletal muscle mass index (SMI), calculated from appendicular lean mass, measured using a bioimpedance device.1 Recently, we proposed creatinine-to-cystatin C ratio (CCR), calculated using circulating levels of creatinine and cystatin C as a simple marker of muscle mass and fat infiltration in the muscle (myosteatosis), an indicator of muscle quality.2,3 However, whether the CCR was just a proxy of the SMI or represented different muscle properties from the SMI was unclear.