This module explores the clinical role of cystatin C in estimating glomerular filtration rate (GFR) and its application in the evaluation and management of chronic kidney disease (CKD). It reviews the strengths and limitations of creatinine- and cystatin C-based GFR estimation, discusses current guideline recommendations supporting the use of cystatin C, and examines situations where the two biomarkers provide differing estimates of kidney function. Through published evidence and practical clinical cases, the session highlights how cystatin C can support more accurate CKD diagnosis and staging, improve risk assessment, and inform medication dosing in selected patient populations. The content is relevant for nephrologists, internists, primary care physicians, clinical pathologists, laboratory medicine professionals, pharmacists, and other healthcare professionals involved in kidney disease diagnosis and management.