BACKGROUND AND OBJECTIVES: The most common bariatric surgery is Roux-en-Y 
gastric bypass (RYGB), which has been associated with hyperoxaluria and 
nephrolithiasis. We report a novel association of RYGB with renal insufficiency 
as a result of oxalate nephropathy.
DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS: Eleven cases of oxalate 
nephropathy after RYGB were identified from the Renal Pathology Laboratory of 
Columbia University. The clinical features, pathologic findings, and outcomes 
are described.
RESULTS: Patients were predominantly white (72.7%) with a mean age of 61.3 yr. 
Indications for RYGB included morbid obesity (eight patients) and reconstruction 
after total gastrectomy for gastric cancer (three patients). All 11 patients had 
a history of hypertension, and 9 were diabetic. Patients presented with acute 
renal failure, often superimposed on mild chronic renal insufficiency (n = 7), 
at a median of 12 mo after RYGB. The mean creatinine at baseline, at discovery 
of acute renal failure, and at biopsy was 1.5, 5.0, and 6.5 mg/dl, respectively. 
Renal biopsies revealed diffuse tubular degenerative changes, abundant tubular 
calcium oxalate deposits, and varying degrees of tubulointerstitial scarring. In 
addition, seven biopsies had underlying diabetic glomerulosclerosis and two had 
glomerulosclerosis attributable to obesity and hypertension. Eight of 11 
patients rapidly progressed to ESRD and required hemodialysis at a mean of 3.2 
wk after renal biopsy. The remaining three patients were left with significant 
chronic kidney disease.
CONCLUSIONS: Oxalate nephropathy is an underrecognized complication of RYGB and 
typically results in rapid progression to ESRD. Patients with pre-existing renal 
disease may be at higher risk for this complication.