When equations disagree: the impact of creatinine-based eGFR in CKD diagnosis and reclassification

Chronic kidney disease (CKD) is a major global health issue, often underdiagnosed due to its asymptomatic progression. Estimated glomerular filtration rate (eGFR) equations are essential for CKD diagnosis and management, but their performance varies across populations and age groups. This study aimed to compare three validated eGFR equations by assessing their impact on CKD classification and patient reclassification in a Romanian adult population. We retrospectively analyzed 135,630 creatinine results from adult patients admitted to a tertiary care hospital in Romania (2021-2023). eGFR was calculated using CKD-EPI 2009, CKD-EPI 2021, and European Kidney Function Consortium (EKFC) equations. Patients were categorized by age and sex, and classified according to KDIGO GFR stages. Reclassification analysis was focused on two medical decision limits: 60, 30 and 15mL/min/1.73 m². Significant differences in CKD staging were observed across equations. CKD-EPI 2021 consistently led to up-classification of GFR category, with up to 29% of patients over 40 years reclassified into less severe stages. In contrast, EKFC assigned more elderly patients, especially women over 65 years, to stage G3a. Correlation between equations ranged from moderate to strong (τ = 0.59-0.88), with better agreement in older age groups. Reclassification was most frequent around the 60 mL/min/1.73 m² threshold. The choice of eGFR equation substantially impacts CKD classification and may influence clinical decision-making and diagnosis. While EKFC and CKD-EPI 2021 correlate with CKD-EPI 2009, they produce divergent staging patterns. Further validation using measured GFR and outcome data is needed.