Hypocitraturia is one of the major risk factors for nephrocalcinosis in very low birth weight (VLBW) infants

Abstract

Background. Very low birth weight (VLBW) infants are at risk to develop nephrocalcinosis (NC). NC may result from spontaneous or therapy-induced imbalance between promoters and inhibitors of crystallization in the urine. However, data on "normal" urinary excretions of these parameters in VLBW infants are sparse. Therefore, we prospectively examined the urinary excretion of calcium, oxalate, uric acid, and citrate in VLBW infants during the first 8 weeks of life. Methods. Urine samples were collected once weekly in 124 VLBW infants. NC appeared in 16 infants, whose data were separately analyzed. The remaining 108 infants were divided into subgroups: A, <1000 g (N = 53); and B, 1000 to 1500 g (N = 55). Random urine samples were analyzed and the results were expressed as molar creatinine ratios. Calcium/citrate and oxalate/citrate expressed the risk for calcium oxalate crystallization. Results. In group A, citrate excretion was lower at weeks 2 to 5 and 7; calcium/citrate was higher in weeks 2, 4, and 7; oxalate/citrate was higher in weeks 3, 4, 7, and 8; and calcium/ creatinine ratio was higher in week 4 (P < 0.05). Citrate/creatinine ratios were low in nine infants with NC. Oxalate/creatinine and calcium/creatinine were elevated in five and calcium/ citrate was increased in nine infants with NC. Conclusion. Hypocitraturia is a major risk factor for NC in VLBW infants, especially in those <1000 g. The urinary excretions in VLBW infants seem to depend on birth weight, age, and clinical condition. Hence, supplementation with alkali citrate may have a beneficial effect in the prevention of NC.