Hyperoxaluria after modern bariatric surgery: case series and literature review

Two recent studies have shown that modern bariatric surgery leads to significant hyperoxaluria and risk of nephrolithiasis. However, neither report evaluates the use or effects of stone risk modifying agents in these patients. We sought to determine the impact of medical management on stone risk profile in patients who have undergone Roux-en-y gastric bypass.

Twenty-four-hour urine collections of all patients referred to a tertiary clinic for nephrolithiasis in the past 4 years were reviewed. Those patients with severe (>75 mg/day) hyperoxaluria were identified. Retrospective chart review was performed to identify those patients with a history of bariatric surgery. Student's t-test was used to compare mean urinary parameters between bariatric and non-bariatric patients.

Out of all stone formers within our 24-h urine collection database, 39 patients had severe hyperoxaluria (oxalate >75 mg/day). Twenty-six patients had complete information for review. Five patients had a history of bariatric surgery. Compared with non-bariatric patients, those with a history of bariatric surgery had increased use of oral calcium (80 vs. 28%) and citrate supplementation (100 vs. 47%), higher urinary oxalate (129 vs. 91 mg/day) and volume (2.9 vs. 2.4 L/day), lower urinary citrate (390 vs. 800 mg/day) and calcium (155 vs. 235 mg/day), and a decreased supersaturation of calcium oxalate (6.7 vs. 11).

Appropriate medical management, in particular oral calcium and citrate supplementation, and perhaps most importantly aggressive fluid intake can mitigate some of the effects of enteric hyperoxaluria caused by fat malabsorption after modern bariatric surgery.