PURPOSE: Nephrolithiasis and renal failure secondary to severe hyperoxaluria 
were complications of jejunoileal bypass for obesity, leading to the 
discontinuation of this procedure in the United States in 1980. Bariatric 
procedures currently in use have not been adequately evaluated for this 
complication.
MATERIALS AND METHODS: We compared 24-hour urine chemistry studies of 132 
patients with nephrolithiasis who had undergone bariatric surgery with the urine 
chemistry studies of patients who had undergone jejunoileal bypass, those with 
routine kidney stones and normal subjects. The primary aim was to determine if 
hyperoxaluria developed in patients who underwent bariatric surgery and had 
kidney stones as had been seen with jejunoileal bypass.
RESULTS: Patients who have undergone modern bariatric surgery had an adjusted 
mean urine oxalate excretion of 83 mg per day compared to 39 mg per day for 
routine kidney stone formers and 34 mg per day for normal subjects (p <0.001 for 
both comparisons), but not quite as high as that found in patients treated with 
jejunoileal bypass (102 mg per day, p <0.001). Urine supersaturation of calcium 
oxalate, the main driving force for calcium oxalate stone formation, was higher 
in patients treated with bariatric surgery compared to routine kidney stone 
formers and normal subjects (p <0.001 for both comparisons).
CONCLUSIONS: Hyperoxaluria is the most significant abnormality of urine 
chemistry studies in patients with kidney stones who have undergone bariatric 
surgery. Many of these patients have a degree of hyperoxaluria that could lead 
to kidney failure. Further studies are required to determine the prevalence of 
this problem in patients who have undergone bariatric surgery.