Prevalence of hyperoxaluria after bariatric surgery

Abstract

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.

Figure 1

Urine oxalate excretion by group. A, oxalate excretion in patients with bariatric surgery, routine stone formers and nonstone forming participants. Asterisks indicate p <0.001 vs bariatric surgery. B, oxalate excretion in patients with RY (RYGB) and those with DS. Data are shown as least mean square using ANOVA with creatinine, gender and weight included in model as covariates. Asterisk indicates p <0.001 vs RY.

Figure 2

Urine oxalate variation. A, average urine oxalate excretion for 2 collections did not correlate with time since bariatric surgery. Solid line indicates linear regression (r = 0.00, p = not significant). B, oxalate excretion on urine collection days 1 and 2. Dashed line indicates linear regression (r = 0.77, p <0.001). Solid line indicates line of identity. d, day.