For millions of adults living with—or unknowingly at risk of—chronic kidney disease, the single number that determines their diagnosis, medication dosing, and transplant eligibility may be less reliable than most clinicians assume. The gap between estimated and measured kidney filtration is not merely academic; it has direct consequences for how patients are staged, treated, and monitored.
Glomerular filtration rate (GFR) sits at the center of chronic kidney disease (CKD) classification under the internationally adopted KDIGO framework, which uses GFR thresholds alongside albuminuria levels to stratify patients across disease stages. In everyday clinical settings, true measured GFR (mGFR)—the reference standard—is rarely obtained because it requires timed urine collection or exogenous filtration markers, is time-consuming, and lacks widespread availability. Instead, estimated GFR (eGFR), derived from serum creatinine or cystatin C with demographic adjustments, serves as a practical proxy. The concern highlighted in this JAMA analysis is that even minor numerical discrepancies between eGFR equations can push borderline patients across staging thresholds, triggering meaningfully different clinical pathways for chemotherapy dosing, antimicrobial adjustment, cardiovascular risk assessment, and transplant eligibility.
This analysis lands at a particularly consequential moment in nephrology. The 2021 revision of eGFR equations—removing race as a coefficient—was a landmark equity correction, but it also renewed scrutiny of how well any equation captures true filtration across diverse populations, body compositions, and comorbidity profiles. Research comparing creatinine-based versus cystatin C-based eGFR equations consistently shows systematic disagreement in specific subgroups, including the elderly and those with abnormal muscle mass. The practical implication is that single-equation reliance creates structured classification error at the margins. While confirmatory mGFR remains too burdensome for routine use, the case for dual-biomarker eGFR reporting—combining creatinine and cystatin C—is strengthening and merits broader clinical adoption. This is an incremental but clinically significant contribution to an ongoing diagnostic precision debate.