Since serum creatinine concentrations are more reliant on muscle mass compared to cystatin C levels, the serum creatinine-cystatin C (Cr/CysC) ratio has been suggested to relate to muscle mass across different patient populations, which include older adults [10], cancer patients [11], and those with chronic kidney disease (CKD) not undergoing dialysis [12]. Here, CST3 is linked to chronic kidney disease.