Oxalate nephropathy in association with gastric bypass.

We present the case of a 46-year-old woman with a history of Roux-en-Y gastric bypass one year prior, who presented to the emergency room with vomiting and oliguria lasting 10 days. Initial evaluation revealed acute kidney injury with serum creatinine 14.9 mg/dL (normal range 0.5-0.9), serum urea 240 mg/dL (normal range 17-49), proteinuria 0.10 g/day and a glomerular filtration rate less than 10 ml/min per 1.73 m2. Urine sediment showed 15-20 leukocytes and 25 red blood cells per field, with no cylinders or crystals observed. A renal biopsy was performed, and pathology showed oxalate crystals in renal tubules and interstitial fibrosis, confirming the diagnosis of oxalate nephropathy. Despite the administration of intravenous sodium bicarbonate, red blood cell transfusions and high doses of loop diuretics, renal failure persisted, as evidenced by the presence of oliguria, serum creatinine 13.5 mg/dL, serum urea 220 mg/dL and serum phosphate 8 mg/dL (normal range 2.5-4.5), and hemodialysis therapy was initiated 3 days after admission to the hospital until the present time. Increased oxalate absorption secondary to fat malabsorption due to bypass gastric causes hyperoxaluria, crystal deposition and oxalate nephropathy. The aim of this report is to highlight the strong correlation between oxalate nephropathy and bariatric surgery, with their implications.