Association of Hypercalciuria and Nephrocalcinosis in Very Low Birth Weight Premature Infants: Significance of Spot Urinary Calcium/Creatinine Ratio in Early Detection and Prevention

Background Nephrocalcinosis (NC) and hypercalciuria (HC) are frequent findings in very low birth weight (VLBW) infants and may contribute to long-term kidney complications. The spot urinary calcium-to-creatinine ratio (Ca/Cr) is a simple tool for detecting HC, but its usefulness in early NC prediction remains uncertain. Methods We retrospectively analyzed 205 VLBW infants admitted to a tertiary neonatal intensive care unit between 2012 and 2021. Demographic, clinical, and laboratory data were collected. Serial spot urine Ca/Cr ratios were measured, and NC was diagnosed by renal ultrasonography. Infants were compared according to the presence or absence of NC. Statistical analyses included Chi-square, Mann–Whitney U, and ROC curve analysis. Results NC was identified in 29.8% of infants. Those with NC had lower gestational age and were more often male. A positive family history of kidney stones was strongly associated with NC. Mean Ca/Cr ratios prior to NC diagnosis and peak Ca/Cr values were significantly higher in infants with NC. A Ca/Cr cut-off of ≥0.5 mg/mg was significantly associated with NC (sensitivity 85.4%, specificity 32.1%). Vitamin D supplementation patterns did not differ between groups. Conclusions In VLBW infants, a spot urinary Ca/Cr ratio ≥0.5 mg/mg is associated with NC and may serve as an early, easily obtainable screening marker. Incorporating Ca/Cr monitoring into routine follow-up may support earlier identification of at-risk infants and guide preventive strategies. Prospective studies are warranted to validate these findings.