Comparison of Established and Emerging Biomarkers Across Estimated GFR

Established and emerging kidney biomarkers reflect filtration, tubular injury, inflammation, or cellular stress, but their relationships with estimated glomerular filtration rate (eGFR) are incompletely characterized. TRUE-GFR was a prospective cross-sectional study of 200 adults undergoing elective renal scintigraphy. Twelve serum or urinary biomarkers were measured, and eGFR was calculated using Chronic Kidney Disease Epidemiology Collaboration (CKD-EPI) creatinine, cystatin C, and combined creatinine–cystatin C equations. Among biomarkers not incorporated into the equations, urea showed the strongest and most consistent correlations across all three eGFR definitions (r = −0.733 to −0.795). Kidney injury molecule-1 (KIM-1), proenkephalin A 119–159 (penKid), and soluble urokinase-type plasminogen activator receptor (suPAR) showed moderate associations, strongest for cystatin C-based and combined eGFR. Neutrophil gelatinase-associated lipocalin (NGAL) correlated moderately with cystatin C-based eGFR (r = −0.505) but weakly with creatinine-based eGFR (r = −0.241). Cysteine-rich protein 1 (CRIP1) correlations were weak, and urinary NephroCheck was unrelated to eGFR. These findings characterize concordance with estimated GFR and should not be interpreted as comparative diagnostic accuracy for true glomerular filtration.