One estimated glomerular filtration rate, many diseases: What remains beyond filtration‐based classification of chronic kidney disease?

Estimated glomerular filtration rate (eGFR) is indispensable for detecting, staging, prognosticating, and managing chronic kidney disease (CKD), but it measures filtration rather than defining the underlying disease. A reduced eGFR can reflect many different processes, including nephron loss, altered renal hemodynamics, glomerular injury, tubulointerstitial disease, vascular damage, congenital abnormalities, obstruction, systemic inflammation, recurrent acute kidney injury, or combinations of these mechanisms. Thus, patients with the same eGFR may have different kidneys, diseases, trajectories, prognoses, and treatment opportunities. Current CKD classification already incorporates cause, GFR category, and albuminuria category, but in clinical practice and research eGFR often remains disproportionately influential in language, referral pathways, trial eligibility, and treatment decisions. This simplification can obscure active or treatable disease, encourage over‐investigation of stable vascular or age‐related impairment, and create biologically heterogeneous trial populations that dilute treatment effects. Albuminuria substantially improves risk stratification, but it does not by itself define disease phenotype or mechanism. This review argues for broader implementation of the cause–GFR–albuminuria framework and for interpreting eGFR within a broader clinical and biological phenotype. A more comprehensive assessment should integrate albuminuria or proteinuria, urine sediment, longitudinal eGFR and albuminuria trajectories, hemodynamic context, medication and nephrotoxin exposure, systemic features, family history, kidney imaging, and targeted use of cystatin C, serology, monoclonal protein testing, genetic testing, kidney biopsy, and molecular biomarkers when clinically appropriate. The aim is not to replace eGFR but to place it in context. Precision nephrology will depend on distinguishing filtration level from disease identity, activity, chronicity, reversibility, and treatment responsiveness.