The effect of gastric banding on kidney stone disease

Delta weight loss unlike genetic variation associates with hyperoxaluria after malabsorptive bariatric surgery

The risk of enteric hyperoxaluria is significantly increased after malabsorptive bariatric surgery (MBS). However, its underlying determinants are only poorly characterized. In this case-control study, we aimed at identifying clinical and genetic factors to dissect their individual contributions to the development of post-surgical hyperoxaluria. We determined the prevalence of hyperoxaluria and nephrolithiasis after MBS by 24-h urine samples and clinical questionnaires at our obesity center. Both hyperoxaluric and non-hyperoxaluric patients were screened for sequence variations in known and candidate genes implicated in hyperoxaluria (AGXT, GRHPR, HOGA1, SLC26A1, SLC26A6, SLC26A7) by targeted next generation sequencing (tNGS). The cohort comprised 67 patients, 49 females (73%) and 18 males (27%). While hyperoxaluria was found in 29 patients (43%), only one patient reported postprocedural nephrolithiasis within 41 months of follow-up. Upon tNGS, we did not find a difference regarding the burden of (rare) variants between hyperoxaluric and non-hyperoxaluric patients. However, patients with hyperoxaluria showed significantly greater weight loss accompanied by markers of intestinal malabsorption compared to non-hyperoxaluric controls. While enteric hyperoxaluria is very common after MBS, genetic variation of known hyperoxaluria genes contributes little to its pathogenesis. In contrast, the degree of postsurgical weight loss and levels of malabsorption parameters may allow for predicting the risk of enteric hyperoxaluria and consecutive kidney stone formation.

Effect of preoperative metabolic profiling to reduce the risk of kidney stones after bariatric surgery in patients with a history of stone formation

BACKGROUND

Roux-en-Y gastric bypass (RYGB) is associated with an increased risk of kidney stone formation. This is not observed after sleeve gastrectomy (SG).

OBJECTIVES

Aim of this study was to assess whether preoperative metabolic profiling is helpful in selecting the most optimal bariatric procedure for patients with a kidney stone history.

SETTING

General hospital, the Netherlands.

METHODS

Patients with a kidney stone history and in the run up to bariatric surgery were screened with non-contrast abdominal computed tomography (CT), serum profiling, and 24-hour urine analysis. Those with stones on radiologic imaging and/or high preoperative urinary oxalate were advised to undergo SG instead of RYGB. Pre- and postoperative urine and serum profile differences between both groups were evaluated retrospectively.

RESULTS

Postoperatively, RYGB (N = 28, M:F = 8:20) was associated with a 23.5% reduction in urinary volume, a 85% increase in urinary oxalate excretion with a 230% increase in calcium oxalate (CaOx) supersaturation and a 62% decrease in urinary citrate. Although SG (N = 30, M:F = 12:18) was also associated with a reduction in urinary volume, it had no adverse effects on urinary oxalate and citrate excretion, nor on calcium oxalate supersaturation (CaOx-SS). Both RYGB and SG showed favorable effects on postoperative sodium, calcium, uric acid, and phosphate excretion.

CONCLUSIONS

This study indicates that preoperative metabolic profiling is important to select the optimal bariatric procedure in patients with an a priori increased risk of kidney stone development. These patients should be strongly encouraged to undergo SG instead of RYGB to prevent progressive or recurrent kidney stone disease.

The Beneficial Effects of Bariatric-Surgery-Induced Weight Loss on Renal Function

Obesity represents an independent risk factor for the development of chronic kidney disease (CKD), leading to specific histopathological alterations, known as obesity-related glomerulopathy. Bariatric surgery is the most effective means of inducing and maintaining sustained weight loss. Furthermore, in the context of bariatric-surgery-induced weight loss, a reduction in the proinflammatory state and an improvement in the adipokine profile occur, which may also contribute to the improvement of renal function following bariatric surgery. However, the assessment of renal function in the context of obesity and following marked weight loss is difficult, since the formulas adopted to estimate glomerular function use biomarkers whose production is dependent on muscle mass (creatinine) or adipose tissue mass and inflammation (cystatin-c). Thus, following bariatric surgery, the extent to which reductions in plasma concentrations reflect the actual improvement in renal function is not clear. Despite this limitation, the available literature suggests that in patients with hyperfiltration at baseline, GFR is reduced following bariatric surgery, whereas GFR is increased in patients with decreased GFR at baseline. These findings are also confirmed in the few studies that have used measured rather than estimated GFR. Albuminuria is also decreased following bariatric surgery. Moreover, bariatric surgery seems superior in achieving the remission of albuminuria and early CKD than the best medical treatment. In this article, we discuss the pathophysiology of renal complications in obesity, review the mechanisms through which weight loss induces improvements in renal function, and provide an overview of the renal outcomes following bariatric surgery.

Association of Kidney Stone Disease (KSD) with Primary Gastrointestinal Surgery: a Systematic Review over Last 2 Decades

PURPOSE OF REVIEW

We aim to provide an up-to-date literature review to further characterise the association of kidney stone disease (KSD) with gastrointestinal (GI) surgery. As KSD is associated with significant morbidity, it is important to quantify and qualify this association to provide better care and management for the patient subgroup.

OBJECTIVE

To perform a systematic review of the existing literature to evaluate the association of KSD following GI surgery.

METHODS

A literature search was performed of the following databases: MEDLINE, EMBASE, Scopus, Google Scholar, Key Urology, Uptodate and Cochrane Trials from January 2000 to June 2020.

RECENT FINDINGS

A total of 106 articles were identified, and after screening for titles, abstracts and full articles, 12 full papers were included. This involved a total of 9299 patients who underwent primary GI surgery. Over a mean follow-up period of 5.4 years (range: 1-14.4 years), 819 (8.8%) developed KSD, varying from 1.2 to 83% across studies. The mean time to stone formation was approximately 3 years (range: 0.5-9 years). In the 4 studies that reported on the management of KSD (n = 427), 38.6% went on to have urological intervention. There is a high incidence of KSD following primary GI surgery, and after a mean follow-up of 3 years, around 9% of patients developed KSD. While the GI surgery was done for obesity, inflammatory bowel disease or cancer, the risk of KSD should be kept in mind during follow-up, and prompt urology involvement with metabolic assessment, medical and or surgical management offered as applicable.

Urolithiasis and sleeve gastrectomy: a prospective assessment of urinary biochemical variables

INTRODUCTION

to evaluate urinary biochemical alterations related to urolithogenesis processes after sleeve gastrectomy (SG).

MATERIALS AND METHODS

: prospective study with 32 individuals without previous diagnosis of urolithiasis who underwent SG. A 24-h urine test was collected seven days prior to surgery and at 6-month follow-up. The studied variables were urine volume, urinary pH, oxalate, calcium, citrate, and magnesium and calcium oxalate super saturation (CaOx SS).

RESULTS

patients were mainly women (81.2%), with mean age of 40.6 years. Mean pre- and postoperative BMI were 47.1 ± 8.3 Kg/m2 and 35.5 ± 6.1 Kg/m2, respectively (p<0.001). Urine volume was significantly lower at the postoperative evaluation in absolute values (2,242.50 ± 798.26 mL x 1,240.94 ± 352.39 mL, p<0.001) and adjusted to body weight (18.58 ± 6.92 mL/kg x 13.92 ± 4.65 mL/kg, p<0.001). CaOx SS increased significantly after SG (0.11 ± 0.10 x 0.24 ± 0.18, p<0.001). Moreover, uric acid levels were significantly lower at the postoperative evaluation (482.34 ± 195.80 mg x 434.75 ± 158.38 mg, p=0.027). Urinary pH, oxalate, calcium, citrate, and magnesium did not present significant variations between the pre- and postoperative periods.

CONCLUSION

SG may lead to important alterations in the urinary profile. However, it occurs in a much milder way than that of RYGB.

Nephrolithiasis after bariatric surgery: A comparison of laparoscopic Roux-en-Y gastric bypass and sleeve gastrectomy

INTRODUCTION

Laparoscopic Roux-en-Y gastric bypass (LRYGB) is known to increase risk for calcium oxalate nephrolithiasis due to hyperoxaluria; however, nephrolithiasis rates after laparoscopic sleeve gastrectomy (LSG) are not well described. Our objective was to determine the rate of nephrolithiasis after LRYGB versus LSG.

METHODS

The electronic medical records of patients who underwent LRYGB or LSG between 2001 and 2017 were retrospectively reviewed.

RESULTS

1,802 patients were included. Postoperative nephrolithiasis was observed in 133 (7.4%) patients, overall, and 8.12% of LRYGB (122/1503) vs. 3.68% of LSG (11/299) patients (P < 0.001). Mean time to stone formation was 2.97 ± 2.96 years. Patients with a history of UTI (OR = 2.12, 95%CI 1.41-3.18; P < 0.001) or nephrolithiasis (OR = 8.81, 95%CI 4.93-15.72; P < 0.001) were more likely to have postoperative nephrolithiasis.

CONCLUSION

The overall incidence of symptomatic nephrolithiasis after bariatric surgery was 7.4%. Patients who underwent LRYGB had a higher incidence of nephrolithiasis versus LSG. Patients with a history of stones had the highest risk of postoperative nephrolithiasis.

Nutritional and Micronutrient Care of Bariatric Surgery Patients: Current Evidence Update

PURPOSE OF REVIEW

The continued success of bariatric surgery to treat obesity and obesity-associated metabolic conditions creates a need for a strong understanding of clinical nutrition both before and after these procedures.

RECENT FINDINGS

Surgically induced alteration of gastrointestinal physiology can affect the nutrition of individuals, especially among those who have undergone malabsorptive procedures. While uncommon, a subset of patients may develop protein-calorie malnutrition. In these cases, nutrition support should be tailored to the severity of malnutrition. Among all patients who undergo bariatric surgery, high rates of micronutrient deficiencies have been observed. To mitigate these deficiencies, empiric supplementation with multivitamins, calcium citrate, and vitamin D is generally recommended. Periodic surveillance should be performed for commonly deficient micronutrients, including thiamin (B1), folate (B9), cobalamin (B12), iron, and vitamin D. Following Roux-en-Y gastric bypass, serum levels of copper and zinc should also be monitored. In addition, lipid-soluble vitamins should be monitored following biliopancreatic diversion with/without duodenal switch.

Kidney Stones After Bariatric Surgery: Risk Assessment and Mitigation

Obesity is rampant across the spectrum of age, gender, and race in the Unites States. Paralleling this epidemic, kidney stone prevalence is also rising, affecting nearly 1 in 11 individuals. Bariatric surgical procedures, such as Roux-en-Y gastric bypass (RYGB) and sleeve gastrectomy (SG), are the most effective weight loss options for morbidly obese or severely obese individuals with comorbidities. A number of studies have linked kidney stone development to bariatric surgical history, particularly RYGB, which portends up to a threefold increase in calcium oxalate stone risk compared with age-matched, obese controls. Stone development after malabsorptive (RYGB) and restrictive (SG) bariatric procedures are driven primarily by alterations in 24-h urine profiles, such as increased urinary oxalate, decreased urine volume, and reduced urinary citrate levels-all of which have been linked to increased kidney stone risk. What clinical recommendations, if any, can be given to reduce kidney stone risk in bariatric kidney stone patients? This review provides not only updated stone incidence and 24-h urine data in this population, but also reassurance-the metabolic alterations that result from bariatric surgery can be successfully mitigated by increased provider awareness, patient education, and a combination of dietary and pharmacological adjustments.

Nephrolithiasis after bariatric surgery: A review of pathophysiologic mechanisms and procedural risk

Obesity alone is a known risk factor for nephrolithiasis, and bariatric surgery has been linked to a higher incidence of post-operative new-onset nephrolithiasis. The mean interval from bariatric surgery to diagnosis of nephrolithiasis, ranges from 1.5 to 3.6 years. The stone risk is greatest for purely malabsorptive procedures, intermediate for Roux-en-Y gastric bypass and lowest for purely restrictive procedures (laparoscopic adjustable gastric banding, laparoscopic sleeve gastrectomy) where it approaches or is reduced below that of non-operative obese controls. A history of nephrolithiasis and increasing age at the time of surgery are both associated with an increased risk of new stone formation post-operatively. The underlying pathophysiologic changes following bariatric surgery include increased colonic absorption of oxalate leading to hyperoxaluria, hypocitraturia and increased urinary calcium oxalate supersaturation, which predispose to stone formation. The majority of incident stones are medically managed, with some requiring interventions in the form of lithotripsy or ureteroscopy.

Urolithiasis in inflammatory bowel disease and bariatric surgery

AIM

To analyse current literature focusing on pathogenesis and therapeutic aspects of urolithiasis with inflammatory bowel disease (IBD) and following bariatric surgery.

METHODS

A systematic literature search was performed using PubMed, supplemented with additional references. Studies assessing the association of IBD or bariatric surgery with renal stones in both paediatric and adulthood were included.

RESULTS

Certain types of stones are seen more frequently with IBD. Hyperoxaluria and hypocitraturia are the main metabolic changes responsible for urolithiasis. The incidence of renal stones in malabsorptive types of bariatric surgery such as gastric bypass is high; this is not as common in modern restrictive surgical methods. Preventative methods and urine alkalinisation have been shown to be beneficial.

CONCLUSION

Both conditions are associated with renal stones. Patients’ counselling and prevention strategies are the mainstay of urolithiasis management in these patients.

From chronic kidney disease to kidney transplantation: The impact of obesity and its treatment modalities

Obesity is associated with worse short-term outcomes after kidney transplantation but the effect on long-term outcomes is unknown. Although some studies have reported worse outcomes for obese recipients when compared to recipients with a BMI in the normal range, obese recipients who receive a transplant have better outcomes than those who remain wait-listed. Whether transplant candidates should be advised to lose weight before or after transplant has been debated and this is mainly due to the gap in the literature linking pre-transplant weight loss with better outcomes post-transplantation. The issue is further complicated by the use of BMI as a metric of body fat, the obesity paradox in dialysis patients and the different ethical viewpoints of utility versus equity. Measures used to reduce weight loss, including orlistat and bariatric surgery (in particular those with a malabsorptive component), have been associated with enteric hyperoxaluria with consequent risk of nephrolithiasis and oxalate nephropathy. In this review, we discuss the evidence regarding the use of weight loss measures in the kidney transplant candidate and recipient with a view to recommending whether weight loss should be pursued before or after kidney transplantation.

Risk of nephrolithiasis, hyperoxaluria, and calcium oxalate supersaturation increased after Roux-en-Y gastric bypass surgery: a systematic review and meta-analysis

BACKGROUND

Earlier publications have shown renal stone complications after bariatric surgery. Multiple reports have also linked metabolic changes that alter the urinary chemistry profiles, especially hyperoxaluria, after bariatric surgery. However, evidence on change of other urine chemistry studies and type of bariatric surgery and risk of stone has been inconclusive so far.

OBJECTIVES

To explore the association between bariatric surgery and postoperative urinary chemistry change and risk of stone formation SETTING: A systematic review and meta-analysis.

METHODS

We comprehensively searched the databases of MEDLINE, EMBASE, and the Cochrane Central Register of Controlled Trials (CENTRAL) from their dates of inception to January 2016. The inclusion criteria were published studies of association between bariatric surgery and postoperative renal stone formation or urine chemistry profiles. We used random-effects model meta-analysis and calculated the pooled risk of renal stone and difference in 24-hour urine chemistry profiles.

RESULTS

Twelve observational studies were included in the meta-analysis. There was significantly higher risk of stone formation after Roux-en-Y gastric bypass surgery with pooled relative risk = 1.79 (95% CI: 1.54-2.10). In the analysis of urine chemistry profiles, there was significantly higher calcium oxalate supersaturation, lower citrate, and lower volume postoperatively compared with preoperatively. There was also higher urine oxalate in patients who had bariatric surgery compared with nonsurgery controls.

CONCLUSIONS

Roux-en-Y gastric bypass surgery is associated with higher risk of renal stone and increased urine oxalate and calcium oxalate supersaturation.

The effects of bariatric surgery on bone and nephrolithiasis

The impact of bariatric surgery on cardiovascular and diabetic complications associated with an improvement in survival has overshadowed the adverse skeletal health and development of kidney stone disease in this population. All longitudinal based studies in the literature reporting the incidence of bone fractures or kidney stones following bariatric surgery were reviewed. Moreover, all publications over the past decade which assessed changes in bone mineral density and bone quality, or explored underlying pathophysiologic mechanisms of bone and kidney stone disease were carefully reviewed. This review provides sufficient data to support that osteoporotic fractures and kidney stone disease are associated with Roux-en-Y gastric bypass surgery. However, due to the limited data available to date, no definitive conclusion could yet be drawn whether sleeve gastrectomy or adjustable gastric banding is associated with bone fractures and kidney stones. Bariatric surgery has emerged as the most effective and sustained treatment for weight reduction. This treatment modality has been recognized to diminish the risk of cardiovascular morbidity and mortality and ameliorate diabetes mellitus complications. The derangement in mineral metabolism has emerged as a major complication following bariatric surgery.

The management of patients with enteric hyperoxaluria

Enteric hyperoxaluria is a common occurrence in the setting of fat malabsorption, usually due to intestinal resection or intestinal bypass surgery. Enhanced intestinal absorption of dietary oxalate leads to elevated renal oxalate excretion, frequently in excess of 100 mg/d (1.14 mmol/d). Patients are at increased risk of urolithiasis and loss of kidney function from oxalate nephropathy. Fat malabsorption causes increased binding of diet calcium by free fatty acids, reducing the calcium available to precipitate diet oxalate. Delivery of unabsorbed bile salts and fatty acids to the colon increases colonic permeability, the site of oxalate hyper-absorption in enteric hyperoxaluria. The combination of soluble oxalate in the intestinal lumen and increased permeability of the colonic mucosa leads to hyperoxaluria. Dietary therapy consists of limiting oxalate and fat intake. The primary medical intervention is the use of oral oxalate binding agents such as calcium salts to reduce free intestinal oxalate levels. Bile acid sequestrants can be useful in patients with ileal resection and bile acid malabsorption. Oxalate degrading bacteria provided as probiotics are being investigated but as of yet, no definite benefit has been shown with currently available preparations. The current state of medical therapy and potential future directions will be summarized in this article.

Kidney stones are common after bariatric surgery

Obesity, a risk factor for kidney stones and chronic kidney disease (CKD), is effectively treated with bariatric surgery. However, it is unclear whether surgery alters stone or CKD risk. To determine this we studied 762 Olmsted County, Minnesota residents who underwent bariatric surgery and matched them with equally obese control individuals who did not undergo surgery. The majority of bariatric patients underwent standard Roux-en-Y gastric bypass (RYGB; 78%), with the remainder having more malabsorptive procedures (very long limb RYGB or biliopancreatic diversion/duodenal switch; 14%) or restrictive procedures (laparoscopic banding or sleeve gastrectomy; 7%). The mean age was 45 years with 80% being female. The mean preoperative body mass index (BMI) was 46.7 kg/m(2) for both cohorts. Rates of kidney stones were similar between surgery patients and controls at baseline, but new stone formation significantly increased in surgery patients (11.0%) compared with controls (4.3%) during 6.0 years of follow-up. After malabsorptive and standard surgery, the comorbidity-adjusted hazard ratio of incident stones was significantly increased to 4.15 and 2.13, respectively, but was not significantly changed for restrictive surgery. The risk of CKD significantly increased after the malabsorptive procedures (adjusted hazard ratio of 1.96). Thus, while RYGB and malabsorptive procedures are more effective for weight loss, both are associated with increased risk of stones, while malabsorptive procedures also increase CKD risk.

Kidney stone risk following modern bariatric surgery

Over the past 10 years, a variety of reports have linked bariatric surgery to metabolic changes that alter kidney stone risk. Most of these studies were retrospective, lacked appropriate controls, or involved bariatric patients with a variety of inclusion criteria. Despite these limitations, recent clinical and experimental research has contributed to our understanding of the pathophysiology of stone disease in this high-risk population. This review summarizes the urinary chemistry profiles that may be responsible for the increased kidney stone incidence seen in contemporary epidemiological bariatric studies, outlines the mechanisms of hyperoxaluria and potential therapies through a newly described experimental bariatric animal model, and provides a focused appraisal of recommendations for reducing stone risk in bariatric stone formers.

Update on the evaluation of repeated stone formers

Office management of stone disease is an important component of a urologist's practice. Evaluation should include analysis of stone composition, 24-hour urine studies, identification of modifiable risk factors, and targeted dietary, lifestyle, and/or medical therapy. A sizeable portion of investigated etiologies and risk factors for stone disease have centered on the complex interplay between obesity, diabetes, and other disease states that comprise the metabolic syndrome. Alternatives to traditional preventive therapy, such as probiotics and various fruit juices, are still being studied but may prove useful adjuncts to traditional preventive therapy, where the mainstays remain increased fluid intake, dietary modification, and pharmacologic therapy. Future studies on preventive therapy of urolithiasis are likely to focus on strategies to increase compliance, cost-effectiveness, and systems-based implementation.

Enteric oxalate nephropathy in the renal allograft: an underrecognized complication of bariatric surgery

Enteric hyperoxalosis is a recognized complication of bariatric surgery, with consequent oxalate nephropathy leading to chronic kidney disease and occasionally end-stage renal failure. In patients with prior gastrointestinal bypass surgery, renal allografts are also at risk of oxalate nephropathy. Further, transplant recipients may be exposed to additional causes of hyperoxalosis. We report two cases of renal allograft oxalate nephropathy in patients with remote histories of bariatric surgery. Conservative management led to improvement of graft function in one patient, while the other patient returned to dialysis. Interpretation of serologic, urine and biopsy studies is complicated by oxalate accumulation in chronic renal failure, and heightened excretion in the early posttransplant period. A high index of suspicion and careful clinicopathologic correlation on the part of transplant nephrologists and renal pathologists are required to recognize and treat allograft oxalate nephropathy. As the incidence of obesity and pretransplant bariatric surgery increases in the transplant population, allograft oxalate nephropathy is likely to be an increasing cause of allograft dysfunction.

The effect of restrictive bariatric surgery on urolithiasis

BACKGROUND AND PURPOSE

Roux-en-Y gastric bypass (RYGB) surgery, a mixed malabsorptive/restrictive procedure, is associated with enteric hyperoxaluria and an increased risk of kidney stones. The incidence of nephrolithiasis after purely restrictive bariatric procedures such as adjustable gastric banding or sleeve gastrectomy has not been well described. We aim to analyze the incidence of kidney stones in patients who undergo either adjustable gastric banding or sleeve gastrectomy.

PATIENTS AND METHODS

In a retrospective study, we analyzed a pool of 332 patients who underwent adjustable gastric banding and 85 patients who underwent sleeve gastrectomy at the University of California, San Diego Center for the Treatment for Obesity within a 54-month period (September 2006 to February 2011). The primary outcomes of urinary calculus diagnosis and surgical treatment were investigated using manual chart review and International Classification of Diseases and Related Health Problems-9 code electronic search.

RESULTS

Within the adjustable gastric banding cohort, we found a person-time incidence rate of 3.40 stone diagnoses per 1000 person-years. Within the sleeve gastrectomy cohort, we found a person-time incidence rate of 5.25 stone diagnoses per 1000 person-years.

CONCLUSIONS

Questions remain whether purely restrictive bariatric procedures such as sleeve gastrectomy or adjustable gastric banding avoid the risk of kidney stones. Our study demonstrates a very low incidence of kidney stones after restrictive bariatric procedures, although larger sample sizes, longer follow-up times, and controlled prospective studies are necessary to validate this finding.

The impact of renal function on outcomes of bariatric surgery

The effect of CKD on the risks of bariatric surgery is not well understood. Using the American College of Surgeons National Surgical Quality Improvement Program Participant Use File, we analyzed 27,736 patients who underwent bariatric surgery from 2006 through 2008. Before surgery, 34 (0.12%) patients were undergoing long-term dialysis. Among those not undergoing dialysis, 20,806 patients (75.0%) had a normal estimated GFR or stage 1 CKD, 5011 (18.07%) had stage 2 CKD, 1734 (6.25%) had stage 3 CKD, 94 (0.34%) had stage 4 CKD, and 91 (0.33%) had stage 5 CKD. In an unadjusted analysis, CKD stage was directly associated with complication rate, ranging from 4.6% for those with stage 1 CKD or normal estimated GFR to 9.9% for those with stage 5 CKD (test for trend, P<0.001). Multivariable logistic regression demonstrated that CKD stage predicts higher complication rates (odds ratio for each higher CKD stage, 1.30) after adjustment for diabetes and hypertension. Although patients with higher CKD stage had higher complication rates, the absolute incidence of complications remained <10%. In conclusion, these data demonstrate higher risks of bariatric surgery among patients with worse renal function, but whether the potential benefits outweigh the risks in this population requires further study.

Urolithiasis risk factors in the bariatric population undergoing gastric bypass surgery

BACKGROUND

Previous studies have suggested an increased risk of forming symptomatic urolithiasis after Roux-en-Y gastric bypass (RYGB) attributed to the development of hyperoxaluria. The objective of our investigation was to evaluate changes in the urine milieu after RYGB that might explain the increased risk of urolithiasis.

METHODS

Patients underwent serum and urine chemistry tests 1 week before and 6 months after RYGB at a university hospital. The postoperative urolithiasis risk factors were compared with the preoperative values. Statistical analysis was performed using paired t tests. Significant changes were identified as P ≤ .05.

RESULTS

A total of 38 patients (7 men and 31 women) submitted samples both before and after RYGB. The mean patient weight had decreased from 131 kg to 92 kg. The mean serum creatinine decreased from .83 to .72 mg/dL (P = .0004). Urinary changes known to increase the risk of urolithiasis include a decrease in volume (2-1.5 L/d, P = .03), an increase in calcium (139-182 mg/d, P = .04), and an increase in oxalate (38-48 mg/d, P < .001). The urinary supersaturation indexes for calcium oxalate (4.9-10.5, P < .001) increased.

CONCLUSION

Our results confirm that patients undergoing RYGB develop changes in the urinary milieu predisposing them to forming urinary stones. Urolithiasis risk is multifactorial and is related to more than just hyperoxaluria. A patient's long-term risk of developing stones and the effect on renal function is unknown. Preoperative counseling of patients regarding their risk of forming stones and dietary counseling to minimize their risk of developing stones postoperatively is warranted.

Bariatric surgery and renal function

Obesity causes a significant healthcare burden and has been shown to be an important risk factor in the development of cardiovascular disease, type 2 diabetes, and increasingly chronic kidney disease. Bariatric surgery is the most effective treatment for obesity and has been shown to drastically improve both blood pressure and diabetic control. However, the interaction of bariatric surgery and renal function is less clear. This review focuses on the effect of bariatric surgery on renal function both in the acute situation, with respect to acute kidney injury, and also on changes in renal function parameters post-bariatric surgery weight loss. The interaction of obesity, bariatric surgery, and nephrolithiasis as a precipitant of acute kidney injury will also be considered. The role of bariatric surgery in pre- and post-renal transplant recipients is discussed as well as possible mechanisms underlying the improvement in renal function.

Metabolic syndrome and bariatric surgery in stone disease etiology

PURPOSE OF REVIEW

To review the prevalence and mechanisms of stone formation in patients with metabolic syndrome and in those submitted to bariatric surgery.

RECENT FINDINGS

MetS is associated with urinary stone disease, which appears to be sustained by dietetic factors and insulin resistance. The latter represented in obesity and diabetes favors uric acid precipitation in urine via a more acidic urinary load. Patients submitted to modern bariatric surgery are at risk of nephrolithiasis and nephropathy as a consequence of malabsorption and hyperoxaluria, which are more consistent after Roux-en-Y gastric bypass than after gastric banding. Other stone risk factors such as hypocitraturia may also be present.

SUMMARY

Patients with metabolic syndrome and those submitted to modern bariatric surgery are both at risk of nephrolithiasis and nephropathy. Accurate stone screening careful monitoring of renal function and diet counseling are strongly encouraged in these patients.

Urinary tract stones

Urinary tract stone disease is one of the most common urologic conditions in the US, with a lifetime prevalence of about 13% for men and 7% for women. In this article we review the management of urinary tract stones and discuss when to seek urologic consultation. We cover epidemiologic data, stone types, presenting symptoms, imaging, metabolic evaluation and risk factors, and medical management strategies. We also discuss the indications for surgical intervention and the common operative procedures currently available.

Bariatric surgery and renal function: a precarious balance between benefit and harm

Medical treatment of obesity and lifestyle modification have limited effectiveness in treating it in morbidly obese individuals. Importantly, bariatric surgery is regarded as the only therapy that is effective in maintaining significant weight loss in morbidly obese individuals. Despite the fact that bariatric surgery-induced weight loss is associated with a significant decrease in morbidity and mortality and improvement in renal function, bariatric surgery has recently been shown to be associated with a significant risk of nephrolithiasis. The main risk factor for nephrolithiasis is increased excretion of urinary oxalate. In this review, we discuss the association between bariatric surgery, an increased risk of renal stone formation and oxalate nephropathy.