Etiology of nephrocalcinosis in preterm neonates: Association of nutritional intake and urinary parameters

Background. Nephrocalcinosis (NC) in preterm neonates has been described fr equently, and small-scale studies suggest an unfavorable effect on renal fu nction. The etiologic factors have not yet been fully clarified. We perform ed a prospective observational study to identify factors that influence the development of NC. Methods. The study population consisted of 215 preterm neonates with a gest ational age <32 weeks. Clinical characteristics and intake in the first fou r weeks of calcium, phosphorus, vitamin D, protein, and ascorbic acid were noted. Serum calcium, phosphate, vitamin D, magnesium, uric acid, creatinin e, urea and urinary calcium, phosphate, oxalate, citrate, magnesium, uric a cid, and creatinine were assessed at four weeks of age and at term. Renal u ltrasonography (US) was performed at four weeks and at term. At term was de fined as a postconceptional age of 38 to 42 weeks. Results. NC was diagnosed by means of US in 33% at four weeks and in 41% at term. Patients with NC at four weeks had a significantly higher mean intak e of calcium (P < 0.05), phosphorus (P < 0.05), and ascorbic acid (P < 0.01 ) than patients without NC. They had a higher mean serum calcium (2.55 vs. 2.46 mmol/L, P < 0.01) and a higher mean urinary calcium/creatinine ratio ( 2.6 vs. 2.1 mmol/mmol, P < 0.05). Patients with NC at term had a lower birt h weight (1142 vs. 1260 g, P < 0.05) and a lower gestational age (28.8 vs. 29.4 weeks, P < 0.05), were treated significantly longer with furosemide, d examethasone, theophylline, and thiazides, developed chronic lung disease m ore frequently (40 vs. 16%, P < 0.001), and had a higher mean urinary calci um/creatinine ratio (2.7 vs. 2.3 mmol/mmol, P < 0.05) and a lower mean urin ary citrate/calcium ratio (1.1 vs. 1.7 mmol/mmol, P = 0.005). Conclusions. NC develops as a result of an imbalance between stone-inhibiti ng and stone-promoting factors. A high intake of calcium, phosphorus, and a scorbic acid, a low urinary citrate/calcium ratio, a high urinary calcium/c reatinine ratio, immaturity, and medication to prevent or treat chronic lun g disease with hypercalciuric side effects appear to contribute to the high incidence of NC in preterm neonates.