Stone composition, metabolic profile and the presence of the gut-inhabiting bacterium Oxalobacter formigenes as risk factors for renal stone formation.

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).