A sarcopenia index based on serum creatinine and cystatin C cannot accurately detect either low muscle mass or sarcopenia in urban community-dwelling older people

The aim of this study was to evaluate the diagnostic value of the sarcopenia index (serum creatinine [mg/dl]/cystatin C [mg/dl] × 100) for estimating low muscle mass and sarcopenia in community-dwelling older adults. We included 371 older adults (≥60 years) with normal kidney function. Four common diagnostic criteria (the European Working Group on Sarcopenia in Older People (EWGSOP), Asia Working Group for Sarcopenia (AWGS), International Working Group on Sarcopenia (IWGS), and Foundation for the National Institutes of Health (FNIH) criteria) were separately applied as the “gold standard”. The receiver operating characteristic (ROC) curves and the area under the ROC curves (AUC) were applied to evaluate the overall diagnostic accuracy. For identifying low muscle mass, the AUC ranged from 0.505 (95% confidence interval [CI] 0.453–0.557) to 0.558 (95% CI 0.506–0.609). For identifying sarcopenia, the AUC ranged from 0.555 (95% CI 0.503–0.606) to 0.618 (95% CI 0.566–0.668). Subgroup analyses according to gender showed similar results. In conclusion, the sarcopenia index based on serum creatinine and cystatin C may not serve as biomarkers of either low muscle mass or sarcopenia in urban community-dwelling older people with normal kidney function.