Oxalate and calcium excretion in cystic fibrosis

BACKGROUND: A patient with cystic fibrosis (CF) and repeated calcium oxalate renal stones prompted us to investigate other children for risk factors for this recognised complication of CF. METHODS: Twenty four hour urinary excretion of calcium, oxalate, and glycolate was measured in children with CF and no symptoms of renal tract stones. Normal diet and treatments were continued. RESULTS: In 26 children (aged 5-15.9 years) oxalate excretion was correlated with age; 14 of 26 children had oxalate excretion above an age appropriate normal range. There was a positive correlation between oxalate excretion and glycolate excretion. Mean calcium excretion was 0.06 mmol/kg/24 h with 21 of 24 children having calcium excretion below the normal range. CONCLUSIONS: Hyperoxaluria may reflect malabsorption although correlation between excretion of oxalate and glycolate suggests a portion of the excess oxalate is derived from metabolic processes. The hypocalciuria observed here may protect children with CF from renal stones.