Gastric band placement for obesity is not associated with increased urinary risk of urolithiasis compared to bypass. J Urol. 2009;182:2340-2346. [PMID: 19762051 DOI: 10.1016/j.juro.2009.07.041]

Opportunities in Primary and Enteric Hyperoxaluria at the Cross-Roads Between the Clinic and Laboratory

Hyperoxaluria is a condition in which there is a pathologic abundance of oxalate in the urine through either hepatic overproduction (primary hyperoxaluria [PH]) or excessive enteric absorption of dietary oxalate (enteric hyperoxaluria [EH]). Severity can vary with the most severe forms causing kidney failure and extrarenal manifestations. To address the current challenges and innovations in hyperoxaluria, the 14th International Hyperoxaluria Workshop convened in Perugia, Italy, bringing together international experts for focused presentation and discussion. The objective of the following report was to disseminate an overview of the proceedings and provide substrate for further thought. The format of this paper follows the format of the meeting, addressing, "PH type 1" (PH1) first, followed by "surgery, genetics, and ethics in PH", then "PH types 2 and 3," (PH2 and PH3) and, finally, "EH." Each session began with presentations of the current clinical challenges, followed by discussion of the latest advances in basic and translational research, and concluded with interactive discussions about prioritizing the future of research in the field to best serve the need of the patients.

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.

Prospective Assessment of the Prevalence of Enter Hyperoxalosis in Kidney Transplant Candidates

Enteric hyperoxalosis (EH) is an emerging cause of kidney transplantation (KT) dysfunction. We sought to determine the prevalence of EH and factors that affect plasma oxalate (POx) among at-risk KT candidates.

Methods

We prospectively measured POx among KT candidates evaluated at our center from 2017 to 2020 with risk factors for EH namely bariatric surgery, inflammatory bowel disease, or cystic fibrosis. EH was defined by a POx ≥10 μmol/L. Period-prevalence of EH was calculated. We compared mean POx across 5 factors: underlying condition, chronic kidney disease (CKD) stage, dialysis modality, phosphate binder type, and body mass index.

Results

Of 40 KT candidates screened, 23 had EH for a 4-y period prevalence of 58%. Mean POx was 21.6 ± 23.5 μmol/L ranging from 0 to 109.6 μmol/L. 40% of screened had POx >20 μmol/L. Sleeve gastrectomy was the most common underlying condition associated with EH. Mean POx did not differ by underlying condition (P = 0.27), CKD stage (P = 0.17), dialysis modality (P = 0.68), phosphate binder (P = 0.58), and body mass index (P = 0.56).

Conclusions

Bariatric surgery and inflammatory bowel disease were associated with a high prevalence of EH among KT candidates. Contrary to prior studies, sleeve gastrectomy was also associated with hyperoxalosis in advanced CKD. POx concentrations observed in EH reached levels associated with tissue and potentially allograft deposition. Concentrations can be as high as that seen in primary hyperoxaluria. More studies are needed to assess if POx is indeed a modifiable factor affecting allograft function in patients with EH.

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.

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.

The Risks of Stone Diagnosis and Stone Removal Procedure After Different Bariatric Surgeries

Introduction: Nephrolithiasis is common after malabsorptive bariatric surgery; however, the comparative risk of stone formation after different bariatric surgeries remains unclear. We seek to compare the risk of stone diagnosis and stone procedure after gastric banding (GB), sleeve gastrectomy (SG), short-limb Roux-en-Y (SLRY), long-limb Roux-en-Y (LLRY), and biliopancreatic diversion with duodenal switch (BPDDS). Patients and Methods: Using an administrative database, we retrospectively identified 116,304 patients in the United States, who received bariatric surgery between 2007 and 2014, did not have a known kidney stone diagnosis before surgery, and were enrolled in the database for at least 1 year before and after their bariatric surgery. We used diagnosis and procedural codes to identify comorbidities and events of interest. Our primary analysis was performed with extended Cox proportional hazards models using time to stone diagnosis and time to stone procedure as outcomes. Results: The adjusted hazard ratio of new stone diagnosis from 1 to 36 months, compared to GB, was 4.54 for BPDDS (95% confidence interval [CI] 3.66-5.62), 2.12 for LLRY (95% CI 1.74-2.58), 2.15 for SLRY (95% CI 2.02-2.29), and 1.35 for SG (95% CI 1.25-1.46). Similar results were observed for risk of stone diagnosis from 36 to 60 months, and for risk of stone removal procedure. Male sex was associated with an overall 1.63-fold increased risk of new stone diagnosis (95% CI 1.55-1.72). Conclusions: BPDDS was associated with a greater risk of stone diagnosis and stone procedures than SLRY and LLRY, which were associated with a greater risk than restrictive procedures. Nephrolithiasis is more common after more malabsorptive bariatric surgeries, with a much greater risk observed after BPDDS and for male patients.

Bariatric Surgery in Patients with a History of Nephrolithiasis: 24-h Urine Profiles and Radiographic Changes After Roux-en-Y Gastric Bypass Versus Sleeve Gastrectomy

BACKGROUND

To evaluate the differences in 24-h urine profiles, radiographic imaging, and stone events post-Roux-en-Y gastric bypass versus sleeve gastrectomy in patients with a history of nephrolithiasis.

METHODS

A retrospective review was conducted on 102 patients with a history of nephrolithiasis who then underwent bariatric surgery at our tertiary academic center. Computed tomography imaging and 24-h urine profile values were performed pre-operatively and at 1-year follow-up.

RESULTS

A total of 60 patients underwent Roux-en-Y gastric bypass and 42 had sleeve gastrectomy. The Roux-en-Y gastric bypass group had significant increases in oxalate and decreases in citrate (p = 0.009 and 0.003, respectively), while the sleeve gastrectomy group had decreases in oxalate and stable citrate (p = 0.013 and 0.906, respectively). Roux-en-Y gastric bypass was the only significant predictor of post-operative hyperoxaluria (OR 7.1 [95% CI 2.3-21.3], p = 0.001). Radiographically, 38.3% of the Roux-en-Y gastric bypass group and 26.2% of the sleeve gastrectomy group had an increase in stone burden, and post-operative stone procedure rate was 10.0% and 7.1%, respectively.

CONCLUSIONS

At 1-year post-bariatric surgery, patients who underwent Roux-en-Y gastric bypass had exacerbated lithogenic urinary profiles, while those in sleeve gastrectomy patients improved. Although not statistically significant, stone burden increase and stone procedure rate were higher post-Roux-en-Y gastric bypass and will likely worsen at a longer follow-up due to the group's lithogenic 24-h urine profiles. These findings support pre-bariatric counseling and urinary monitoring in patients with a history of kidney stones who undergo RYGB, with a multi-disciplinary approach between urologists and general surgeons.

Risk Factors for Kidney Stone Formation following Bariatric Surgery

Kidney stones are painful, common, and increasing in incidence. Obesity and bariatric surgery rates are also on the rise in the United States. Although bariatric surgery is associated with improvements in metabolic outcomes, malabsorptive bariatric surgery procedures are also associated with increased risk of kidney stones. Restrictive bariatric surgeries have not been associated with kidney-stone risk. Higher risk of kidney stones after malabsorptive procedures is associated with postsurgical changes in urine composition, including high urine oxalate, low urine citrate, and low urine volume. Certain dietary recommendations after surgery may help mitigate these urine changes and reduce risk of kidney stones. Understanding risk of kidney stones after surgery is essential to improving patient outcomes after bariatric surgery.

Metabolic syndrome and liver disease in the era of bariatric surgery: What you need to know!

Metabolic syndrome (MS) is defined as the constellation of obesity, insulin resistance, high serum triglycerides, low high-density lipoprotein cholesterol, and high blood pressure. It increasingly affects more and more people and progressively evolves into a serious issue with widespread healthcare, cost, and quality of life associated consequences. MS is associated with increased morbidity and mortality due to cardiovascular or chronic liver disease. Conservative treatment, which includes diet, exercise, and antidiabetic agents, is the mainstay of treatment, but depends on patient compliance to medical treatment and adherence to lifestyle modification recommendations. Bariatric surgery has recently emerged as an appropriate alternative treatment with promising long-term results. Sleeve gastrectomy and Roux-en-Y gastric bypass constitute the most commonly performed procedures and have been proven both cost-effective and safe with low complication rates. Liver transplantation is the only definitive treatment for end-stage liver disease and its utilization in patients with non-alcoholic steatohepatitis has increased more than fivefold over the past 15 years. In this review, we summarize current state of evidence on the surgical treatment of MS.

Enteric hyperoxaluria: role of microbiota and antibiotics

PURPOSE OF REVIEW

Enteric hyperoxaluria is commonly observed in malabsorptive conditions including Roux en Y gastric bypass (RYGB) and inflammatory bowel diseases (IBD). Its incidence is increasing secondary to an increased prevalence of both disorders. In this review, we summarize the evidence linking the gut microbiota to the risk of enteric hyperoxaluria.

RECENT FINDINGS

In enteric hyperoxaluria, fat malabsorption leads to increased binding of calcium to free fatty acids resulting in more soluble oxalate in the intestinal lumen. Bile acids and free fatty acids in the lumen also cause increased gut permeability allowing more passive absorption of oxalate. In recent years, there is more interest in the role of the gut microbiota in modulating urinary oxalate excretion in enteric hyperoxaluria, stemming from our knowledge that microbiota in the intestines can degrade oxalate. Oxalobacter formigenes reduced urinary oxalate in animal models of RYGB. The contribution of other oxalate-degrading organisms and the microbiota community to the pathophysiology of enteric hyperoxaluria are also currently under investigation.

SUMMARY

Gut microbiota might play a role in modulating the risk of enteric hyperoxaluria through oxalate degradation and bile acid metabolism. O. formigenes is a promising therapeutic target in this population; however, further studies in humans are needed to test its effectiveness.

Review of post bariatric surgery effects on common genitourinary physiology

Background: Obesity is a worldwide challenging health problem. Weight loss through medical management of obesity has not always been successful, thus, giving rise to the need for surgical intervention. Bariatric surgery has been shown to be helpful for morbidly obese patients. However, studies have also shown the effect of surgery on stone formation, fertility and erectile function. This review summarizes the main findings of several studies that analyze stone formation and fertility in men as well as erectile function post bariatric surgery. The underlying pathophysiologic alterations post bariatric surgery include increased absorption of oxalate leading to hyperoxaluria, hypocitraturia and increased urinary calcium oxalate supersaturation. Contradicting data exist on the effect of bariatric surgery on fertility and erectile function. Further studies are needed to analyze the mechanisms.

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.

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.

Reversal of Gastric Bypass Resolves Hyperoxaluria and Improves Oxalate Nephropathy Secondary to Roux-en-Y Gastric Bypass

Hyperoxaluria after Roux-en-Y gastric bypass (RYGB) increases the risk for kidney injury. Medical therapies for hyperoxaluria have limited efficacy. A 65-year-old female was evaluated for acute kidney injury [AKI, serum creatinine (Cr) 2.1 mg/dl, baseline Cr 1.0 mg/dl]. She did not have any urinary or gastrointestinal symptoms or exposure to nephrotoxic agents. Sixteen months prior to this evaluation, she underwent RYGB for morbid obesity. Her examination was unremarkable for hypertension or edema and there was no protein or blood on urine dipstick. Kidney biopsy revealed acute tubulointerstitial nephritis with oxalate crystals in tubules. The concurrent finding of severe hyperoxaluria (urine oxalate 150 mg/day) confirmed the diagnosis of oxalate nephropathy. Despite medical management of hyperoxaluria, her AKI worsened. Laparoscopic reversal of RYGB was performed and within 1 month, her hyperoxaluria resolved (urine oxalate 20 mg/day) and AKI improved (Cr 1.7 mg/dl). Surgical reversal of RYGB may be considered in patients with oxalate nephropathy at high risk of progression who fail medical therapy. Physicians need to be aware of the possibility of oxalate nephropathy after RYGB and promptly treat the hyperoxaluria to halt further kidney damage.

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.

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.

Enteric hyperoxaluria: an important cause of end-stage kidney disease

Hyperoxaluria is a frequent complication of inflammatory bowel diseases, ileal resection and Roux-en-Y gastric bypass and is well-known to cause nephrolithiasis and nephrocalcinosis. The associated prevalence of chronic kidney disease and end-stage kidney disease (ESKD) is less clear but may be more consequential than recognized. In this review, we highlight three cases of ESKD due to enteric hyperoxaluria following small bowel resections. We review current information on the pathophysiology, complications and treatment of this complex disease.

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.

Urinary evaluation after RYGBP: a lithogenic profile with early postoperative increase in the incidence of urolithiasis

BACKGROUND

The objective of this study was to assess predictors for new-onset stone formers after Roux-en-Y gastric bypass (RYGBP).

METHODS

One hundred and fifty-one obese patients underwent RYGBP and were followed for 1 year. The analysis comprised two study time points: preoperative (T0) and 1 year after surgery (T1). They were analyzed for urinary stones, blood tests, and 24-h urinary evaluation. Nonparametric tests, logistic regression, and multivariate analysis were conducted using SPSS 17.

RESULTS

Median BMI decreased from 44.1 to 27.0 kg/m2 (p < 0.001) in the postoperative period. Urinary oxalate (24 versus 41 mg; p < 0.001) and urinary uric acid (545 versus 645 mg; p < 0.001) increased significantly postoperatively (preoperative versus postoperative, respectively). Urinary volume (1310 versus 930 ml; p < 0.001), pH (6.3 versus 6.2; p = 0.019), citrate (268 versus 170 mg; p < 0.001), calcium (195 versus 105 mg; p < 0.001), and magnesium (130 versus 95 mg; p = 0.004) decreased significantly postoperatively (preoperative versus postoperative, respectively). Stone formers increased from 16 (10.6 %) to 27 (17.8%) patients in the postoperative analysis (p = 0.001). Predictors for new stone formers after RYGBP were postoperative urinary oxalate (p = 0.015) and uric acid (p = 0.044).

CONCLUSIONS

RYGBP determined profound changes in urinary composition which predisposed to a lithogenic profile. The prevalence of urinary lithiasis increased almost 70% in the postoperative period. Postoperative urinary oxalate and uric acid were the only predictors for new stone formers.

Update on oxalate crystal disease

Oxalate arthropathy is a rare cause of arthritis characterized by deposition of calcium oxalate crystals within synovial fluid. This condition typically occurs in patients with underlying primary or secondary hyperoxaluria. Primary hyperoxaluria constitutes a group of genetic disorders resulting in endogenous overproduction of oxalate, whereas secondary hyperoxaluria results from gastrointestinal disorders associated with fat malabsorption and increased absorption of dietary oxalate. In both conditions, oxalate crystals can deposit in the kidney leading to renal failure. Since oxalate is primarily renally eliminated, it accumulates throughout the body in renal failure, a state termed oxalosis. Affected organs can include bones, joints, heart, eyes, and skin. Since patients can present with renal failure and oxalosis before the underlying diagnosis of hyperoxaluria has been made, it is important to consider hyperoxaluria in patients who present with unexplained soft tissue crystal deposition. The best treatment of oxalosis is prevention. If patients present with advanced disease, treatment of oxalate arthritis consists of symptom management and control of the underlying disease process.

Calcium oxalate supersaturation increases early after Roux-en-Y gastric bypass

BACKGROUND

Calcium oxalate (CaOx) nephrolithiasis is an adverse effect of Roux-en-Y gastric bypass surgery (RYGB). It is unknown when the increased risk for CaOx stone formation occurs after surgery.

METHODS

We studied 13 morbidly obese adults undergoing RYGB with 24-hour urine collections at 4 weeks before and 1, 2, 4, and 6 months after surgery and computed CaOx relative saturation ratio (RSR) by EQUIL2.

RESULTS

Eleven patients were female, mean ± standard deviation age was 41.1 ± 7.2 years, and none had diabetes or chronic kidney disease. Median (interquartile range) urinary oxalate excretion increased linearly from 12.6 (10.9-37.9) mg/24 hr at baseline to 28.4 (14.4-44.0) mg/24 hr at 6 months (slope = .188; P = .005). CaOx RSR increased significantly at 2 months after RYGB (1.4 [1.2-2.4] to 4.9 [1.7-10.0]; P = .017) and rose throughout the study to 5.7 (3.7-12.2) at 6 months (P = .001) with a positive linear slope (.255; P = .001). One patient had critical CaOx supersaturation (RSR = 34.7) and severe hyperoxaluria (101.7 mg/24 hr) at 6 months after RYGB. Significant decreases over time were seen in urine volume and sodium and potassium excretion, but no changes were noted in urinary pH, calcium, magnesium, or citrate.

CONCLUSIONS

Our data suggest that CaOx RSR, and thus risk for nephrolithiasis, rises as early as 2 months after RYGB and increases gradually in the first 6 months, largely because of reduced urine volume and increased urinary oxalate excretion. Interventions to reduce CaOx RSR, such as adequate fluid intake and agents to bind enteric oxalate, need to be evaluated in patients at risk for nephrolithiasis after RYGB.

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.

Response to dietary oxalate after bariatric surgery

BACKGROUND AND OBJECTIVES

Bariatric surgery (BS) may be associated with increased oxalate excretion and a higher risk of nephrolithiasis. This study aimed to investigate urinary abnormalities and responses to an acute oxalate load as an indirect assessment of the intestinal absorption of oxalate in this population.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

Twenty-four-hour urine specimens were collected from 61 patients a median of 48 months after BS (post-BS) as well as from 30 morbidly obese (MO) participants; dietary information was obtained through 24-hour food recalls. An oral oxalate load test (OLT), consisting of 2-hour urine samples after overnight fasting and 2, 4, and 6 hours after consuming 375 mg of oxalate (spinach juice), was performed on 21 MO and 22 post-BS patients 12 months after BS. Ten post-BS patients also underwent OLT before surgery (pre-BS).

RESULTS

There was a higher percentage of low urinary volume (<1.5 L/d) in post-BS versus MO (P<0.001). Hypocitraturia and hyperoxaluria (P=0.13 and P=0.36, respectively) were more frequent in BS versus MO patients. The OLT showed intragroup (P<0.001 for all periods versus baseline) and intergroup differences (P<0.001 for post-BS versus MO; P=0.03 for post-BS versus pre-BS). The total mean increment in oxaluria after 6 hours of load, expressed as area under the curve, was higher in both post-BS versus MO and in post-BS versus pre-BS participants (P<0.001 for both).

CONCLUSIONS

The mean oxaluric response to an oxalate load is markedly elevated in post-bariatric surgery patients, suggesting that increased intestinal absorption of dietary oxalate is a predisposing mechanism for enteric hyperoxaluria.

Controlled metabolic diet reduces calcium oxalate supersaturation but not oxalate excretion after bariatric surgery

OBJECTIVE

To identify the effect of a controlled metabolic diet on reducing urinary calcium oxalate (CaOx) supersaturation in subjects with hyperoxaluric nephrolithiasis after potentially malabsorptive forms of bariatric surgery.

METHODS

Subjects with a history of CaOx kidney stones and mild hyperoxaluria after bariatric surgery (n = 9) collected baseline 24-hour urine samples while consuming a free choice diet. They were then instructed to consume a controlled diet low in oxalate (70-80 mg/d), normal in calcium (1000 mg/d), and moderate in protein before 2 final 24-hour urine collections.

RESULTS

Overall, the urinary CaOx supersaturation decreased from 1.97 ± 0.49 delta Gibbs (DG) with the free choice diet to 1.13 ± 0.75 DG with the controlled diet (P < .01). This occurred in the absence of a significant change in urinary oxalate excretion (0.69 ± 0.29 mmol/d with the free choice diet compared with 0.66 ± 0.38 mmol/d with the controlled diet). Urinary volume, citrate, and pH all increased, although not significantly (P > .05), contributing to the significant CaOx supersaturation change.

CONCLUSION

A controlled metabolic diet normal in calcium, moderate in protein, and reduced in oxalate can positively affect urinary CaOx supersaturation after bariatric surgery. However, this diet did not appear to decrease urinary oxalate excretion. Therefore, restriction of dietary oxalate alone might not be enough to reduce urinary oxalate excretion to normal levels in this group of patients with known enteric hyperoxaluria. Additional strategies could be necessary, such as the use of oral calcium supplements as oxalate binders and a lower fat diet.

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.

Biochemical control of bone loss and stone-forming propensity by potassium-calcium citrate after bariatric surgery

BACKGROUND

Patients undergoing Roux-en-Y gastric bypass (RYGB) surgery are prone to developing bone loss and kidney stones. The goal of the present study was to test the hypothesis that an effervescent formulation of potassium calcium citrate (PCC) would avert metabolic complications by providing bioavailable calcium and alkali.

METHODS

A total of 24 patients with RYGB underwent a 2-phase crossover randomized trial comparing PCC and placebo. During the last 2 days of each 2-week phase, the serum and 24-hour urine samples were analyzed for calcium and bone turnover markers, acid base status, and urinary stone risk factors.

RESULTS

Compared with placebo, PCC marginally reduced the serum parathyroid hormone level and significantly decreased urinary deoxypyridinoline by 12% (P <.001) and serum type 1 collagen C-telopeptide by 22% (P <.01). PCC significantly increased the net gastrointestinal alkali absorption, citrate, and pH and significantly lowered the urinary net acid excretion (P <.001). The urinary saturation of uric acid decreased significantly (P <.001). The supersaturation of calcium oxalate and brushite did not change despite an increase in calcium and pH. In untreated urine samples with citrate concentrations altered to mimic those of placebo and PCC, calcium oxalate agglomeration was significantly inhibited by PCC.

CONCLUSION

In RYGB patients, PCC supplementation inhibited bone resorption by providing bioavailable calcium, reduced the urinary saturation of uric acid, and increased the inhibitor activity against calcium oxalate agglomeration by providing alkali that increased urinary pH and citrate.

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.

The effect of restrictive bariatric surgery on urinary stone risk factors

OBJECTIVES

Malabsorptive bariatric procedures such as Roux-en-Y gastric bypass (RYGB) place patients at risk for developing kidney stones. Stone risk factors after purely restrictive procedures such as gastric banding and sleeve gastrectomy are not well characterized. Therefore, we performed a study to examine urinary risk factors of patients who underwent restrictive gastric surgery for bariatric indications.

METHODS

A total of 18 patients were enrolled in the study; 14 underwent gastric banding and 4 underwent sleeve gastrectomy. All subjects collected 24-hour urine specimens; at least 6 months had elapsed between surgery and urine collection. Standard stone risk parameters were assessed, and comparisons were made with a group of normal adult nonstone-formers, routine stone-formers, and RYGB bariatric surgery subjects.

RESULTS

Urinary oxalate excretion of the restrictive cohort was significantly less than the RYGB cohort (35.4 vs. 60.7 mg/d; P <.001) and not significantly different from that of the normal subjects (32.9 mg/d; P = .798) and routine stone-formers (37.2 mg/d; P = .997). There were no other significant differences in urinary parameters.

CONCLUSIONS

Restrictive bariatric surgery does not appear to be associated with an increased risk for kidney stone disease. In particular, urinary oxalate levels were significantly less than those of RYGB subjects and not significantly different from routine stone-formers and nonstone-forming controls.