PURPOSE: Recent investigations have shown increased oxalate excretion in 
patients in whom kidney stones formed after contemporary bariatric surgery. We 
determined whether there is an increased prevalence of hyperoxaluria after such 
procedures performed in nonstone formers.
MATERIALS AND METHODS: A total of 58 nonstone forming adults who underwent 
laparoscopic Roux-en-Y (52) or a biliopancreatic diversion-duodenal switch 
procedure (6) collected 24-hour urine specimens 6 months or greater after 
bariatric surgery. Standard stone risk parameters were assessed. Comparisons 
were made with a group of healthy nonstone forming adults and stone formers in a 
commercial database.
RESULTS: The bariatric group had a significantly higher mean urinary oxalate 
excretion compared to that in controls and stone formers (67.2 vs 34.1 and 37.0 
mg per day, respectively, p <0.001). Mean oxalate excretion of patients who 
underwent a biliopancreatic diversion-duodenal switch procedure was higher than 
in the Roux-en-Y group (90 vs 62 mg per day, p <0.05). There was a significant 
correlation between urine oxalate excretion on the 2 collection days but some 
patients showed significant variability. Of the patients 74% showed 
hyperoxaluria in at least 1, 24-hour urine collection and 26% demonstrated 
profound hyperoxaluria, defined as oxalate excretion more than 100 mg per day, 
in at least 1 collection. This occurred in 3 of the 6 patients in the 
biliopancreatic diversion-duodenal switch group and in 12 of the 52 in the 
Roux-en-Y cohort. Hyperoxaluria was not uniformly expressed.
CONCLUSIONS: There is a high prevalence of hyperoxaluria in patients without a 
history of kidney stones who undergo bariatric surgery. A significant proportion 
of these patients have profound hyperoxaluria, which is not uniformly expressed.