Usefulness of the serum creatinine/cystatin C ratio as a blood biomarker for sarcopenia components among age groups in community‐dwelling older people: The SONIC study

AimThe serum creatinine/cystatin C ratio (CCR) or sarcopenia index is considered a useful marker of muscle mass. However, its usefulness in late‐stage older adults remains unclear. We aimed to determine the usefulness of CCR as an indicator of sarcopenia in community‐dwelling Japanese adults aged >75 years.MethodsOur study recruited participants aged 70, 80, and 90 ± 1 years during the baseline years, and included a 3‐year follow‐up in the Septuagenarians, Octogenarians, Nonagenarians, Investigation with Centenarians study. From 2015 to 2018, 955 participants were eligible: 367 in their 70s, 304 in their 80s, and 284 in their 90s. The diagnostic components of sarcopenia, including “low muscle mass, plus low muscle strength, and/or low physical performance,” were evaluated using the bioelectrical impedance analysis‐measured skeletal muscle mass index (SMI), handgrip strength, and short physical performance battery (SPPB) score, respectively, in accordance with the Asia Working Group for Sarcopenia 2019 criteria. Separate analyses were performed between each component and CCR, adjusting for sex, body mass index, and other blood biomarkers in each group.ResultsThe relationship between CCR and sarcopenia components was significant for handgrip strength (β = 0.21, 0.13, 0.19, and P < 0.0001, =0.0088, <0.0001, for the 70s, 80s, and 90s age groups, respectively); however, it was limited for SMI (β = 0.14; P = 0.0022, only for the 90s) and not significant for the SPPB score.ConclusionCCR is a limited indicator of sarcopenia in late‐stage older adults. Although its association with muscle strength was significant, its relationship with muscle mass and physical performance was less pronounced. Geriatr Gerontol Int 2024; ••: ••–••.