Glomerular filtration rate (GFR) is the cornerstone of kidney function evaluation, underpinning the diagnosis, staging, and monitoring of CKD.1 Current clinical practice generally uses estimated GFR from creatinine (eGFRcr); eGFR from cystatin C (eGFRcys) is recommended as an alternative or confirmatory marker when eGFRcr may be unreliable—such as when serum creatinine is suspected to be influenced by abnormal muscle mass, diet, or medications.1 With the growing use of cystatin C in clinical practice, discordances between eGFRcr or eGFRcys are increasingly encountered, with eGFRcys often being lower than eGFRcr.