Predisposing factors for nephrolithiasis and nephrocalcinosis in cystic fibrosis

Cystic fibrosis (CF) is characterized by chronic pulmonary disease, insufficient pancreatic and digestive function, and abnormal sweat concentration. There is controversy about predisposing factors of nephrolithiasis and nephrocalcinosis in patients with cystic fibrosis. We assessed the results of metabolic evaluation in patients with cystic fibrosis and its correlation with nephrocalcinosis.

Forty five CF patients, mean age 47.1 months, were enrolled in the study. No one had past history of nephrolithiasis and/or nephrocalcinosis. The records were reviewed for clinical characteristics and all patients underwent metabolic evaluation including serum electrolyte measurements and spot urine analysis. Ultrasonography was performed in all patients to detect nephrocalcinosis and urolithiasis.

Nephrocalcinosis was found in 5 (11%) patients. No patient had clinical symptoms of nephrolithiasis and/or micro/macroscopic hematuria. Metabolic evaluation of the CF patients versus normal reference values showed decreased serum uric acid in 48.8%, elevated serum phosphate in 24.4%, and urine oxalate excretion in 51%. Metabolic evaluation of the nephrocalcinosis positive patients versus nephrocalcinosis negative group showed no statistical difference in serum electrolytes. The mean value of urine calcium excretion was lower in patients with nephrocalcinosis (P=0.001). Despite lack of any significant correlation, higher numerical hyperoxaluria was observed in patients with severe steatorrhea. There was no statistical correlation between steatorrhea and urine calcium as well as oxalate excretion.

Hypocalciuria in the nephrocalcinotic CF patients may be seen. It can be hypothesized that hypocalciuria may be due to a primary defect in renal calcium metabolism in CF patients.