Two recent studies have shown that modern bariatric surgery leads to significant hyperoxaluria and risk of nephrolithiasis. However, neither report evaluates the use or effects of stone risk modifying agents in these patients. We sought to determine the impact of medical management on stone risk profile in patients who have undergone Roux-en-y gastric bypass. Twenty-four-hour urine collections of all patients referred to a tertiary clinic for nephrolithiasis in the past 4 years were reviewed. Those patients with severe (>75 mg/day) hyperoxaluria were identified. Retrospective chart review was performed to identify those patients with a history of bariatric surgery. Student’s t-test was used to compare mean urinary parameters between bariatric and non-bariatric patients. Out of all stone formers within our 24-h urine collection database, 39 patients had severe hyperoxaluria (oxalate >75 mg/day). Twenty-six patients had complete information for review. Five patients had a history of bariatric surgery. Compared with non-bariatric patients, those with a history of bariatric surgery had increased use of oral calcium (80 vs. 28%) and citrate supplementation (100 vs. 47%), higher urinary oxalate (129 vs. 91 mg/day) and volume (2.9 vs. 2.4 L/day), lower urinary citrate (390 vs. 800 mg/day) and calcium (155 vs. 235 mg/day), and a decreased supersaturation of calcium oxalate (6.7 vs. 11). Appropriate medical management, in particular oral calcium and citrate supplementation, and perhaps most importantly aggressive fluid intake can mitigate some of the effects of enteric hyperoxaluria caused by fat malabsorption after modern bariatric surgery.

Introduction

Two recent studies have shown that modern bariatric surgery leads to significant hyperoxaluria and risk of nephrolithiasis. However, neither report evaluates the use or effects of stone risk modifying agents in these patients. We sought to determine the impact of medical management on stone risk profile in patients who have undergone Roux-en-y gastric bypass.

Materials and methods

Twenty-four-hour urine collections of all patients referred to a tertiary clinic for nephrolithiasis in the past 4 years were reviewed. Those patients with severe (>75 mg/day) hyperoxaluria were identified. Retrospective chart review was performed to identify those patients with a history of bariatric surgery. Student's t-test was used to compare mean urinary parameters between bariatric and non-bariatric patients.

Results

Out of all stone formers within our 24-h urine collection database, 39 patients had severe hyperoxaluria (oxalate >75 mg/day). Twenty-six patients had complete information for review. Five patients had a history of bariatric surgery. Compared with non-bariatric patients, those with a history of bariatric surgery had increased use of oral calcium (80 vs. 28%) and citrate supplementation (100 vs. 47%), higher urinary oxalate (129 vs. 91 mg/day) and volume (2.9 vs. 2.4 L/day), lower urinary citrate (390 vs. 800 mg/day) and calcium (155 vs. 235 mg/day), and a decreased supersaturation of calcium oxalate (6.7 vs. 11).

Conclusions

Appropriate medical management, in particular oral calcium and citrate supplementation, and perhaps most importantly aggressive fluid intake can mitigate some of the effects of enteric hyperoxaluria caused by fat malabsorption after modern bariatric surgery.

We aimed to assess the impact of oral calcium supplementation (OCS) on the prevalence of nephrolithiasis among a cohort of patients undergoing surgery for primary hyperparathyroidism (PHPT). There were 339 patients undergoing surgery for PHPT with detailed past medical history data that were analyzed. 73 patients (22%) had a history of nephrolithiasis prior to parathyroid surgery. Nephrolithiasis was more common among men than women (40% vs 15%, P < 0.001), despite the predominance of women (73% of patients) with hyperparathyroidism. 83 patients (25%) used OCS. OCS was associated with a lower prevalence of nephrolithiasis (9.6% vs 25.4% without OCS, P = 0.002). This protective effect included both men and women (rates of nephrolithiasis with and without supplements: men 19% vs 46%, P = 0.027; women 7% vs 17%, P = 0.04). The mechanism for the apparent protective effect of OCS on rates of nephrolithiasis is unclear, and further research is required to elucidate the variable penetrance of nephrolithiasis among PHPT patients.

Objectives

Urinary excretion of citrate is dependent on glomerular filtration, tubular reabsorption, and excretion. Acid base status is thought to play a significant role in urinary citrate excretion. It has been assumed that increased urinary citrate will increase urinary pH. The aim of this study was to confirm the association of increased urinary citrate levels with increased urinary pH.

Methods

The 24-hour urine collections of all patients with stones referred to our clinic in the past 4 years were reviewed. The samples were collected and analyzed for routine stone risk profiles by a commercial laboratory (Litholink, Chicago, Ill). The Student t test and analysis of variance were used to compare the mean values as applicable. Pearson's correlations were also calculated for each variable.

Results

A total of 572 patients had at least one 24-hour urine sample from the past 4 years. The mean urinary citrate was 305 mg/day. The mean urinary pH of all patients was 6.14. Statistical evaluation of all patients showed no correlation between urinary citrate and pH (r = -0.04, P = 0.36). In a subset of patients with urinary potassium greater than 100 mEq/day (n = 100), urinary citrate and urinary pH were both increased; however, there was still no correlation between the two (r = 0.011, P = 0.806).

Conclusions

Despite the current dogma that increasing urinary citrate increases urinary pH, in a cohort of patients with urinary stone formation who provided 24-hour urine specimens, no correlation was found between urinary citrate and urinary pH levels.