CST3 and sarcopenia: Given the decreased serum creatinine, but not cystatin C, in patients experiencing muscle wasting, other indices based on these two renal markers, such as the creatinine-to-cystatin C ratio (Cr/CysC), eGFRcys-to-eGFRcre ratio (eGFRcys/eGFRcre), and the difference between eGFRcys and eGFRcre (eGFRcys–eGFRcre), have been reported for the assessment of sarcopenia in various populations (31–39).