Urinary calcium excretion in paediatric population: reference values and hypercalciuria risk factors

A cross-sectional, population based study was carried out to measure the normal calciuria values in healthy school children. A total of 1.259 healthy school children, aged 6 to 14 yr/old, living in 16 different towns of Catalunya were selected after random sampling of schools and systematic sampling of children by school grade. First results showed that calciuria, measured as the calcium/creatinine index in a morning urine sample, is inversely related to age and hence the great majority of high index values were found among children younger than 10 years. After standardising the indexes to 1.73 sq.m. of body surface area, this inverse correlation was corrected and high calciuria values spread evenly through all ages. The 95th percentile of the standardised calciuria/creatininuria index was 0.23. Conclusions: These findings: a) provide normal values of calciuria/creatininuria index, standardised to body surface area, in a healthy paediatric population; b) suggest that age is a confounding factor when computing the calciuria/creatininuria index: c) suggest that idiopathic hypercalciuria could be the result of a combination of hereditary and environmental factors.