Absorptive hyperoxaluria leads to an increased risk for urolithiasis or nephrocalcinosis in cystic fibrosis.

Background: Hyperoxaluria has been incriminated to account for the increased incidence of urolithiasis or nephrocalcinosis in patients with cystic fibrosis (CF). Hyperoxaluria presumably is caused by fat malabsorption and the absence of such intestinal oxalate-degrading bacteria as Oxalobacter formigenes. To better elucidate its pathophysiological characteristics, we prospectively studied patients with CF by determining these parameters and performing renal ultrasonography twice yearly.