Stone Composition, Metabolic Profile and the Presence of the Gut-Inhabiting Bacterium Oxalobacter formigenes as Risk Factors for Renal Stone Formation

Abstract

Objective: To examine stone composition, metabolic evaluation and colonization of Oxalobacter formigenes as risk factors for renal stone formation. Subjects and Methods: Eighty patients with renal stones and 70 healthy controls were enrolled in the study. Of the 80 patients, 48 were first-time stone formers (FSF) and 32 were ‘recurrent’ stone formers (RSF), recurrent indicating 2 or more episodes of stone formation. Stone analysis by X-ray crystallography, 24-hour urine metabolic profile and detection of O. formigenes-specific DNA by PCR were performed for each patient. Detection of O. formigenes was also performed on 45 and urinary metabolic profile on an additional 25 controls. Results: Calcium oxalate monohydrate was the major component of stones, hyperoxaluria and hypocitraturia were the most common urinary abnormalities in the 80 patients, 46% of RSF patients had hypercalciuria. Urinary abnormalities were far less frequent in the controls, with the exception of hypocitraturia (40%). Of the urinary metabolites, only calcium levels were significantly different (p < 0.05) between FSF (6.50 ± 4.08 mmol/24 h) and RSF (8.21 ± 5.26 mmol/24 h) patients. Colonization of O. formigenes was higher in controls (62.2%) than in FSF (33.3%) or RSF (28%) patients, it was least in patients with more than 4 episodes (7%) of stone formation. Conclusion: The findings indicate that lack of colonization of O. formigenes may be an important risk factor for recurrence of stone formation (calcium oxalate monohydrate).