Effect of Gastric Bypass Surgery on Kidney Stone Disease Brian R. Matlaga,* Andrew D. Shore, Thomas Magnuson, Jeanne M. Clark, Roger Johns and Martin A. Makary From the Departments of Urology, Surgery, Anesthesiology and Medicine, the Johns Hopkins University School of Medicine, and the Departments of Health Policy and Management, Johns Hopkins School of Public Health, Baltimore, Maryland Purpose: Recent studies have demonstrated that mineral and electrolyte abnor- Abbreviations malities develop in patients who undergo bariatric surgery. While it is known and Acronyms that these abnormalities are a risk factor for urolithiasis, the prevalence of stone BCBS ϭ Blue Cross Blue Shield disease after bariatric surgery is unknown. We evaluated the likelihood of being BMI ϭ body mass index diagnosed with or treated for an upper urinary tract calculus following Roux-en-Y ϭ gastric bypass surgery. JI jejunoileal Materials and Methods: We identified 4,639 patients who underwent Roux-en-Y RYGB ϭ Roux-en-Y gastric bypass gastric bypass surgery and a control group of 4,639 obese patients who did not have surgery in a national private insurance claims database in a 5-year period (2002 to Submitted for publication October 15, 2008. 2006). All patients had at least 3 years of continuous claims data. Our 2 primary Supported by The Hariri Family Foundation, and Mr. and Mrs. Chad and Nissa Richinson. outcomes were the diagnosis and the surgical treatment of a urinary calculus. The data set used in this study was originally Results: After Roux-en-Y gastric bypass surgery 7.65% (355 of 4,639) of patients created for a different research project on patterns were diagnosed with urolithiasis compared to 4.63% (215 of 4,639) of obese of obesity care within selected BCBS plans. The Ͻ previous research project (but not the current study) patients in the control group (p 0.0001). Subjects in the treatment cohort more was funded by unrestricted research grants from commonly underwent shock wave lithotripsy (81 [1.75%] vs 19 [0.41%], Ethicon Endo-Surgery, Inc. (a Johnson & Johnson p Ͻ0.0001) and ureteroscopy (98 [2.11%] vs 27 [0.58%], p Ͻ0.0001). Logistic company); Pfizer, Inc and GlaxoSmithKline. The data and database development support and guidance regression demonstrated that Roux-en-Y gastric bypass surgery was a significant were provided by the BCBS Association, BCBS of predictor of being diagnosed with a urinary calculus (OR 1.71, CI 1.44–2.04) as Tennessee, BCBS of Hawaii, BCBS of Michigan, well as undergoing a surgical procedure (OR 3.65, CI 2.60–5.14). BCBS of North Carolina, Highmark, Inc. of Pennsyl- Conclusions: vania, Independence Blue Cross of Pennsylvania, Roux-en-Y gastric bypass surgery is associated with an increased Wellmark BCBS of Iowa and Wellmark BCBS of risk of kidney stone disease and kidney stone surgery in the postoperative period. South Dakota. Clinicians should be aware of this hazard and inform patients of this potential * Correspondence: James Buchanan Brady complication. Future studies are needed to evaluate preventive measures in the Urological Institute, The Johns Hopkins University School of Medicine, 600 North Wolfe St., Balti- high risk population. more, Maryland 21287 (telephone: 410-550-3506; FAX: 410-550-3341; e-mail: [email protected]). Key Words: kidney, calculi, bariatric surgery, epidemiology OBESITY has become a leading public result in sustained and significant health epidemic with recent estimates weight loss in the majority of candidate that 30% of American adults are obese morbidly obese patients. In fact, the (BMI greater than 30).1 Even more number of bariatric procedures per- alarming is the trend that prevalence formed in the United States increased rates are increasing rapidly,1 creating a 5-fold from 1998 to 2002.3 deferred societal burden of type II dia- The earliest surgical therapy for betes, heart disease, hypertension, the treatment of obesity was the mal- pregnancy complications, sleep apnea absorptive JI bypass procedure. Al- and other health problems.2 Bariatric though JI bypass did induce rapid surgery is the only therapy to date to and lasting weight loss, increasing ex- our knowledge that has been shown to perience with the procedure led to the 0022-5347/09/1816-2573/0 Vol. 181, 2573-2577, June 2009 ® THE JOURNAL OF UROLOGY Printed in U.S.A. www.jurology.com 2573 Copyright © 2009 by AMERICAN UROLOGICAL ASSOCIATION DOI:10.1016/j.juro.2009.02.029 2574 GASTRIC BYPASS SURGERY AND KIDNEY STONE DISEASE recognition of serious postoperative sequelae such as a BMI greater than 35 and 3 continuous years of followup liver failure, osteomalacia, nephrolithiasis and renal data were selected and assigned an index date of 7 months failure.4 Nephrolithiasis and renal failure were in- after the first month of enrollment to match the median duced by over-absorption of dietary oxalate, which interval between first enrollment and surgery in the treat- resulted in severe hyperoxaluria.5 As a consequence ment group. We excluded from the treatment and control groups female subjects who were pregnant the year be- of these metabolic consequences the JI bypass was fore, the year of or the year following an obese BMI value. abandoned and in 1979 the Food and Drug Admin- We also excluded anyone with a preexisting renal disease 6 istration requested a moratorium on the procedure. diagnosis or who had undergone treatment of an upper The Roux-en-Y gastric bypass overcame many urinary tract calculus (64 and 62 patients, respectively). of the malabsorptive problems associated with JI The 2 groups were matched using the SurveySelect bypass, and is recognized as a safe and effective procedure (SAS®, 2003) on the basis of age (18 to 24, 25 to therapy.3,7 However, some reports have suggested 34, 45 to 54, 55 to 64, 65 to 74 and 75 to 84 years), gender, that patients undergoing certain types of bariatric diagnosis of diabetes or prescription for an antihypergly- surgery such as RYGB are at increased risk for cemic agent at any time before the date of surgery or index postoperative hyperoxaluria. It is not known date, and presence of a diagnosis of hypertension or a whether this hyperoxaluria will ultimately result claim for an antihypertensive medication within 6 months of the surgery/index date. One-to-one sampling with prob- in symptomatic renal calculi as it did in patients 8–10 ability proportional to size was used. undergoing JI bypass. To address this ques- The main dependent variables examined in this study tion we designed a study to measure the preva- were a stone removal procedure (shock wave lithotripsy, lence of kidney stone disease following modern ureteroscopy, nephrolithotomy) and a diagnosis of urinary RYGB surgery performed for bariatric indications. calculi (an exclusion criterion if preexisting). The codes used to define these procedures and conditions can be found in Appendix 2. In terms of analysis simple chi- MATERIALS AND METHODS square tests and logistic regression were performed. SAS® The data and in-kind database development support and version 9.13 was used for all analyses. guidance were provided by the Blue Cross/Blue Shield Association, BCBS of Tennessee, BCBS of Hawaii, BCBS RESULTS of Michigan, BCBS of North Carolina, Highmark, Inc. (of Pennsylvania), Independence Blue Cross (of Pennsylva- We identified 4,639 patients who had undergone nia), Wellmark BCBS of Iowa and Wellmark BCBS of RYGB surgery and met the criteria for the treatment South Dakota. All individuals with 1 of these 7 plans as group as well as a matched control group (table 1). primary insurer were eligible for inclusion in the data set. Females outnumbered males 5-to-1 and the majority The claims data used in this study were de-identified in (64%) of subjects were 35 to 54 years old. An upper accordance with the Health Insurance Portability and Ac- urinary tract calculus was diagnosed in 355 subjects countability Act of 1996 definition of a limited data set and (7.65%) in the bariatric surgery group compared to 215 were used in accordance with federal standards for pro- (4.63%) in the comparison cohort (p Ͻ0.0001). Mean tecting the confidentiality of the personal health informa- time from RYGB to diagnosis of an upper tract calcu- tion of the enrollee. The institutional review board of The lus was 558.65 days. In the subsample who experi- Johns Hopkins University found this analysis to be ex- empt from the requirement for review. The data set in- enced kidney stone events subjects who underwent cludes approximately 2.4 million insured lives during a RYGB were not more likely to have experienced mul- 5-year period (2002 to 2006) with information on enrollee tiple stone events than those in the control cohort (OR age, sex, enrollment dates and claims for reimbursement 1.03, 95% CI 0.736–1.437, p ϭ 0.871). for billable health care services. Included in these data are Of the bariatric surgery cohort 3.30% (153 of patient diagnoses as identified by ICD-9 codes and Diag- 4,639) underwent a urological procedure for an up- nosis Related Groups, and medical procedures classified per urinary tract calculus in the 3 years after bari- by CPT codes and ICD-9 procedure codes. atric surgery vs 0.93% (43 of 4,639) of the compari- Subjects undergoing RYGB surgery with enrollment son group (p Ͻ0.0001) (table 2). Ureteroscopy and for 3 years following the date of bariatric surgery were shock wave lithotripsy were used to a similar extent selected for the treatment group. The codes used to define whereas nephrolithotomy was relied on less com- these procedures are found in Appendix 1. There were 18 patients with cancers of the esophagus, stomach, small monly.