Preterm Infants and Nephrocalcinosis

Nephrocalcinosis (NC), defined as calcification of renal tissue, has been reported to occur in 7-41% of premature infants. Causes of NC are likely multi-factorial, and infants born prematurely and with very low birth weight (\<1500 gm) seem to be at the highest risk of developing NC. Recent changes in recommendations for nutrition for the preterm infant such as higher intakes of protein, calcium, and vitamin D may also play a factor in the pathogenesis of NC. Currently, diagnosis of NC often occurs incidentally during ultrasound evaluation for other issues. Because there is no acute symptom or pattern of symptoms in the preterm population associated specifically with NC, it is possible that many cases of NC may not be diagnosed. Presently, it is impractical and costly to screen all infants for NC with renal ultrasound, therefore there is no standard of care regarding screening for NC. NC may have long-term effects. Studies have shown that preterm infants with NC had shorter kidneys and a lower rate of tubule resorption of phosphorus (TRP) than preterm infants without NC. This study will analyze weekly urinalysis for all enrolled subjects prospectively and then look at the incidence of NC at discharge of the enrolled subjects.