Bladder Stones in Renal Transplant Patients: Presentation, Management, and Follow-up.

INTRODUCTION: The study aim was to analyze the presentation, management, and follow-up of renal transplant patients developing bladder calculi. METHODS: Patients who underwent renal transplant with postoperative follow-up at our institution were retrospectively analyzed (1984-2023) to assess for the development of posttransplant bladder stones. All bladder stones were identified by computerized tomography imaging and stone size was measured using this imaging modality. RESULTS: The prevalence of bladder calculi post-renal transplantation during the study window was 0.22% (N = 20/8,835) with a median time to bladder stone diagnosis of 13 years posttransplant. Of all bladder stone patients, 6 (30%) received deceased donor and 14 (70%) living donor transplants. There were 11 patients with known bladder stone composition available; the most common being calcium oxalate (N = 6). Eleven (55%) patients had clinical signs or symptoms (most commonly microhematuria). Fourteen of the bladder stone cohort patients (70%) underwent treatment including cystolitholapaxy in 12 subjects. Of these 14 patients, 9 (64%) were found to have nonabsorbable suture used for their ureteroneocystostomy closure. CONCLUSIONS: The prevalence of bladder stones post-renal transplant is low. The utilization of nonabsorbable suture for ureteral implantation was the main risk factor identified in our series. This technique is no longer used at our institution. Other factors contributing to bladder stone formation in this population warrant identification.

Forty Years of Oxalobacter formigenes, a Gutsy Oxalate-Degrading Specialist.

Oxalobacter formigenes, a unique anaerobic bacterium that relies solely on oxalate for growth, is a key oxalate-degrading bacterium in the mammalian intestinal tract. Degradation of oxalate in the gut by O. formigenes plays a critical role in preventing renal toxicity in animals that feed on oxalate-rich plants. The role of O. formigenes in reducing the risk of calcium oxalate kidney stone disease and oxalate nephropathy in humans is less clear, in part due to difficulties in culturing this organism and the lack of studies which have utilized diets in which the oxalate content is controlled. Herein, we review the literature on the 40th anniversary of the discovery of O. formigenes, with a focus on its biology, its role in gut oxalate metabolism and calcium oxalate kidney stone disease, and potential areas of future research. Results from ongoing clinical trials utilizing O. formigenes in healthy volunteers and in patients with primary hyperoxaluria type 1 (PH1), a rare but severe form of calcium oxalate kidney stone disease, are also discussed. Information has been consolidated on O. formigenes strains and best practices to culture this bacterium, which should serve as a good resource for researchers.

Disparities in Kidney Stone Disease: A Scoping Review.

PURPOSE: We reviewed the available evidence regarding health disparities in kidney stone disease to identify knowledge gaps in this area. MATERIALS AND METHODS: A literature search was conducted using PubMed®, Embase® and Scopus® limited to articles published in English from 1971 to 2020. Articles were selected based on their relevance to disparities in kidney stone disease among adults in the United States. RESULTS: Several large epidemiological studies suggest disproportionate increases in incidence and prevalence of kidney stone disease among women as well as Black and Hispanic individuals in the United States, whereas other studies of comparable size do not report racial and ethnic demographics. Numerous articles describe disparities in imaging utilization, metabolic workup completion, analgesia, surgical intervention, stone burden at presentation, surgical complications, followup, and quality of life based on race, ethnicity, socioeconomic status and place of residence. Differences in urinary parameters based on race, ethnicity and socioeconomic status may be explained by both dietary and physiological factors. All articles assessed had substantial risk of selection bias and confounding. CONCLUSIONS: Health disparities are present in many aspects of kidney stone disease. Further research should focus not only on characterization of these disparities but also on interventions to reduce or eliminate them.

Future treatments for hyperoxaluria.

PURPOSE OF REVIEW: The review of potential therapies in the treatment of hyperoxaluria is timely, given the current excitement with clinical trials and the mounting evidence of the importance of oxalate in both kidney stone and chronic kidney disease. RECENT FINDINGS: Given the significant contribution of both endogenous and dietary oxalate to urinary oxalate excretions, it is not surprising therapeutic targets are being studied in both pathways. This article covers the existing data on endogenous and dietary oxalate and the current targets in these pathways. SUMMARY: In the near future, there will likely be therapies targeting both endogenous and dietary oxalate, especially in subsets of kidney stone formers.

Dietary oxalate and kidney stone formation.

Dietary oxalate is plant-derived and may be a component of vegetables, nuts, fruits, and grains. In normal individuals, approximately half of urinary oxalate is derived from the diet and half from endogenous synthesis. The amount of oxalate excreted in urine plays an important role in calcium oxalate stone formation. Large epidemiological cohort studies have demonstrated that urinary oxalate excretion is a continuous variable when indexed to stone risk. Thus, individuals with oxalate excretions >25 mg/day may benefit from a reduction of urinary oxalate output. The 24-h urine assessment may miss periods of transient surges in urinary oxalate excretion, which may promote stone growth and is a limitation of this analysis. In this review we describe the impact of dietary oxalate and its contribution to stone growth. To limit calcium oxalate stone growth, we advocate that patients maintain appropriate hydration, avoid oxalate-rich foods, and consume an adequate amount of calcium.