BACKGROUND: Neither the presence nor prevalence of enteric hyperoxaluria has 
been recognized after Roux-en-Y gastric bypass (RYGBP). We have noted a high 
rate of oxalate nephrolithiasis and even 2 patients with oxalate nephropathy in 
this patient population postoperatively. Our aim was to determine the frequency 
of the occurrence and effects of enteric hyperoxaluria after RYGBP.
METHODS: Retrospective review of all patients at our institution diagnosed with 
calcium oxalate nephrolithiasis or oxalate nephropathy after standard (n = 14) 
or distal (n = 9) RYGBP. The mean postoperative follow-up was 55 months.
RESULTS: A total of 23 patients (14 men and 9 women; mean age 45 years; mean 
preoperative body mass index 55 kg/m(2)) developed enteric hyperoxaluria after 
RYGBP, defined by the presence of oxalate nephropathy (n = 2) or calcium oxalate 
nephrolithiasis (n = 21) and increased 24-hour excretion of urinary oxalate 
and/or calcium oxalate supersaturation. Enteric hyperoxaluria was recognized 
after a mean weight loss of 46 kg at 29 months (range 2-85) after RYGBP. Two 
patients developed renal failure and required chronic hemodialysis. Of the 21 
patients with nephrolithiasis, 14 had no history of nephrolithiasis 
preoperatively, and 19 of 21 required lithotripsy or other intervention. Of the 
23 patients, 20 tested had increased oxalate excretion, and 14 of 15 tested had 
high urine calcium oxalate supersaturation.
CONCLUSION: Enteric hyperoxaluria, nephrolithiasis, and oxalate nephropathy must 
be considered with the other risks of RYGBP. Efforts should be made to identify 
factors that predispose patients to developing hyperoxaluria.