1. ¹Department of Internal Medicine, Mayo Clinic College of Medicine, Rochester, Minnesota, USA
2. ²Division of Endocrinology, Diabetes, Metabolism and Nutrition, Department of Internal Medicine, Mayo Clinic College of Medicine, Rochester, Minnesota, USA
3. ³Division of Nephrology and Hypertension, Department of Internal Medicine, Mayo Clinic College of Medicine, Rochester, Minnesota, USA
4. ⁴Mayo Medical School, Mayo Clinic College of Medicine, Rochester, Minnesota, USA
5. ⁵Department of Surgery, Mayo Clinic College of Medicine, Rochester, Minnesota, USA
6. ⁶Department of Biochemistry and Molecular Biology, Mayo Clinic College of Medicine, Rochester, Minnesota, USA
7. ⁷Department of Laboratory Medicine and Pathology, Mayo Clinic College of Medicine, Rochester, Minnesota, USA

Correspondence: JC Lieske, Division of Nephrology and Hypertension, Mayo Clinic College of Medicine, 200 First Street SW, Rochester, Minnesota, 55905, USA. E-mail: Lieske.John@mayo.edu

Received 10 August 2006; Revised 13 January 2007; Accepted 23 January 2007; Published online 21 March 2007.

Abstract

Roux-en-Y bypass surgery is the most common bariatric procedure currently performed in the United States for medically complicated obesity. Although this leads to a marked and sustained weight loss, we have identified an increasing number of patients with episodes of nephrolithiasis afterwards. We describe a case series of 60 patients seen at Mayo Clinic-Rochester that developed nephrolithiasis after Roux-en-Y gastric bypass (RYGB), including a subset of 31 patients who had undergone metabolic evaluation in the Mayo Stone Clinic. The mean body mass index of the patients before procedure was 57 kg/m² with a mean decrease of 20 kg/m² at the time of the stone event, which averaged 2.2 years post-procedure. When analyzed, calcium oxalate stones were found in 19 and mixed calcium oxalate/uric acid stones in two patients. Hyperoxaluria was a prevalent factor even in patients without a prior history of nephrolithiasis, and usually presented more than 6 months after the procedure. Calcium oxalate supersaturation, however, was equally high in patients less than 6 months post-procedure due to lower urine volumes. In a small random sampling of patients undergoing this bypass procedure, hyperoxaluria was rare preoperatively but common 12 months after surgery. We conclude that hyperoxaluria is a potential complicating factor of RYGB surgery manifested as a risk for calcium oxalate stones.