Oxalobacter colonization in the morbidly obese and correlation with urinary stone risk

To establish the baseline preoperative prevalence of Oxalobacter formigenes (OF) colonization in a cohort of obese patients scheduled for Roux-en-Y gastric bypass (RYGB) and determine the effect of OF colonization on urinary oxalate excretion. It has been proposed that loss of OF colonization after RYGB may contribute to the development of hyperoxaluria.

Adult patients scheduled to undergo RYGB were requested to provide a stool specimen and 24-hour urine collection before surgery. OF colonization status was determined by the calcium precipitation test. The 24-hour urine specimens were analyzed by the Litholink Corporation (Chicago, IL).

Of the 51 patients submitting initial stool specimens, only 8 (16%) tested positive for OF, whereas 43 (84%) were negative. Patients colonized with OF were older than uncolonized subjects (52.9±6.8 vs 46.0±10.4 years, P=.03). Urinary oxalate was not significantly different between these groups (P=.14).

OF colonization is uncommon in morbidly obese patients (16%) before surgery. Because hyperoxaluria develops in more than 50% of patients after RYGB, it is unlikely that loss of OF colonization is the primary cause.