How should we assess renal function in neonates and infants?

Aim: Review of current knowledge on assessing renal function in term and preterm neonates. Methods: Literature review and analysis of own data. Results: Prematurity, genetic, environmental and maternal factors may alter peak nephron endowment and life-long renal function. Nephrogenesis continues until 34-36 weeks of gestation, but it is altered with premature delivery. Variability of nephron endowment has a substantial impact on the clearance of renally excreted drugs. Postnatally, glomerular function rate (GFR) increases daily, doubles by two weeks, and slowly reaches full maturity at 18 months of age. Ideally, renal function biomarkers should be expressed as age-independent z-scores, and evidence suggests indexing these values to post-conceptual age rather than chronological age. Newborn and maternal serum creatinine correlate tightly for more than 72 hours after delivery, rendering this biomarker unsuitable for the assessment of neonatal renal function. Cystatin C does not cross the placenta and may be the preferred biomarker in the neonate. Here, we provide preliminary data on the natural evolution of the cystatin C eGFR in infancy. Conclusion: Cystatin C may be superior for GFR estimation in neonates, but the best approach to drug dosing of renally excreted drugs remains to be established.