Enteric Hyperoxaluria, Calcium Oxalate Nephrolithiasis, and Oxalate Nephropathy After Roux-en-Y Gastric Bypass

Roux-en-Y gastric bypass (RYGB) is a popular weight loss surgery for adults with morbid obesity. This chapter reviews potential renal complications caused by abnormalities in oxalate handling after RYGB—i.e., enteric hyperoxaluria, calcium oxalate (CaO x ) nephrolithiasis, and oxalate nephropathy. Hyperoxaluria is an adverse effect of RYGB that occurs due to fat malabsorption and contributes to CaO x nephrolithiasis and oxalate nephropathy. Risk factors for CaO x kidney stones after RYGB include low urine volume, high urine oxalate, and low urine citrate. Oxalate nephropathy is diagnosed by the characteristic kidney biopsy finding of acute tubular injury with oxalate crystals in renal tubules. Therapies to lower urine oxalate include lowering fat and oxalate intake, using calcium supplements to bind oxalate, bile acid sequestrants, or probiotics that degrade intraluminal oxalate. Physicians need to be aware of the possibility of oxalate-mediated renal complications after RYGB, and promptly treat hyperoxaluria to stop kidney damage.