Cystatin C as a Renal Biomarker in Infants with Congenital Anomalies of the Kidney and Urinary Tract (CAKUT): A Systematic Review

Background: The evaluation of renal function in neonates is challenging due to maternal creatinine transfer, reduced muscle mass, and non-steady-state physiology. Cystatin C emerged as a promising biomarker for assessing neonatal glomerular filtration rate. This review summarizes evidence from studies evaluating serum and urine cystatin C in healthy neonates and high-risk groups, including preterm newborns, neonates with acute kidney injury, and those with congenital kidney and urinary tract defects. Methods: Twenty studies were included and qualitatively synthesized following PRISMA guidelines. Results: In the included studies, serum cystatin C exhibited consistent postnatal patterns independent of maternal influence and showed a strong correlation with gestational age and renal development. Cystatin C enabled earlier detection of renal dysfunction compared to serum creatinine, especially in preterm infants and critically ill neonates. In babies with congenital renal abnormalities, cystatin C levels were associated with disease severity and clinical outcomes, while the cystatin C-based estimated glomerular filtration rate surpassed creatinine-based estimations. Urinary cystatin C correlated with tubular damage and increased risk of chronic kidney disease during follow-up. Conclusions: Cystatin C is a reliable biomarker for evaluating neonatal renal function, although further standardization and validation are required for clinical implementation.