Because the negative eGFRdiff could indicate potential sarcopenia, the possibility exists that the marker might have utility beyond kidney function.8,12 Despite the fact that conventional measures typically combine cystatin C and creatinine to derive more accurate eGFRs, we found that the relative difference in calculated GFRs also provided important information and could be used to identify those at high risk of experiencing accelerated frailty and physical function decline in the long term. Here, CST3 is linked to sarcopenia.