Hypercalciuria in ex-preterm children, aged 7-8 years

In a previous study, 8 of 28 ex-preterm infants, aged 4–5 years, had increased urinary calcium excretion. The aim of this study was to confirm this finding and to determine if raised urinary calcium excretion is associated with reduced bone mineralisation. Forty-six ex-preterm children, aged 7–9 years, and 40 age- and sex-matched controls were recruited. The calcium excretion measured from 3 separate 24-h urine collections was recorded and a dietary assessment made from a diary record. Data were retrieved from the neonatal case notes and included aminoglycoside usage. Dual energy X-ray absorptiometry was used to measure bone mineral content and bone mineral density (BMD) in all children. The mean maximum 24-h urinary calcium was significantly higher in the preterm group than the term group (P=0.01). Increased calcium excretion was associated with raised neonatal aminoglycoside levels (P=0.0013). Height standard deviation score and hip BMD were significantly lower in the 21 preterm children with a 24-h urinary calcium above 4 mg/kg per day than term controls (P=0.04 and P=0.004, respectively). Urinary calcium excretion had a negative relationship with hip BMD in the preterm group (P=0.004). This difference in BMD was not observed in the 25 preterm children with normocalciuria. In the 10 preterm girls with hypercalciuria, hip BMD was lower than in control females (P=0.01). This difference in hip BMD between the 11 preterm boys with hypercalciuria and term boys was not significant (P=0.05). In conclusion, preterm children are shorter and have a lower hip BMD than those with normocalciuria. Further prospective studies are required to assess this risk and its influence on subsequent impaired bone mineralisation. Received: 28 September 2000 / Revised: 2 April 2001 / Accepted: 2 April 2001