Background

The incidence of nephrocalcinosis (NC) in ex-premature infants is reported to be high. Although the overall incidence of NC in VLBW infants is reported to be around 20%, ¹ the incidence may approach 50% in infants <750g at birth. ¹ Local data from a group of infants who received dexamethasone for treatment of evolving chronic lung disease showed an incidence of 83%. ²

NC may be a consequence of neonatal treatments such as diuretics and steroids, ¹ or may just be a marker of neonatal illness. Nutritional factors are thought to contribute, particularly high intakes of calcium in the diet which may not necessarily be absorbed and instead are excreted in urine.

Although the natural history of NC is that 66% of infants will have resolution by 15 months of age and 85% by 30 months, ³ some infants will develop renal calculi.  Renal function does not appear to be adversely affected into childhood. ³

Screening Policy

• In view of the potential clinical significance of NC, infants who are <30 weeks at birth should be screened for NC.
• These infants should have a renal ultrasound scan at the same time as their pre-discharge head ultrasound scans (that is, around 36 weeks corrected gestational age, or earlier if ready for discharge prior to this time).

Ultrasound Appearances of Nephrocalcinosis

More marked changes may be seen, with significant calcium deposition in the collecting systems, as below.

Follow-Up

• If significant NC is demonstrated, a referral should be sent to Dr William Wong for follow-up in the Renal Clinic at Starship Hospital

References