Presentation Authors: Joel Hancock*, Xiang Shu, Guixiao Ding, Nicole Miller, Ryan S. Hsi, Nashville, TN
Introduction: Elevated urinary ammonium is found in systemic acidotic states due to renal ammoniagenesis or in the setting of a urease-producing urinary tract infection/colonization due to splitting of urea into bicarbonate and ammonium. As these clinical states associate with kidney stone risk, our objective was to evaluate the clinical characteristics of kidney stone formers with elevated urinary ammonium.
Methods: A retrospective case-control study was performed on kidney stone formers with elevated urinary ammonium (>60mmol/day) on 24-hour urine studies. Patients were seen at our institution from 2006-2017. Inadequate collections determined by creatinine and body mass were excluded. We compared the clinical characteristics, stone compositions, and 24-hour urinary parameters to controls with a history of kidney stones and normal urinary ammonium levels. Subjects were randomly matched 1:1 by age and sex.
Results: One hundred and twenty-one subjects were included in both the study and control cohorts. Mean age in years (Â±SD) was 51.5 (Â±12.9); 83% were male. Compared to controls, the subjects with elevated urinary ammonium levels were more likely to be recurrent stone formers (92% vs. 83%, p=0.029), have a higher BMI (mean 33.5 vs. 29.1, p= < 0.001), higher rates of diabetes (29% vs. 16%, p=0.035), gout (12% vs. 3%, p=0.021), positive urine culture with urease-producing organisms within 6 months of the 24-hour urine collection (18% vs. 8%, p=0.043), recurrent urinary tract infections (21% vs. 10%, p=0.013), a history of bowel resection (20% vs. 3%, p= < 0.001), and a history of urinary reconstructive surgery (10% vs. 2%, p=0.013). Over 90% of stones in both cohorts had a calcium component, while struvite stone composition was more common among subjects with elevated urinary ammonium (6% vs. < 1%, p=0.07). Case subjects had higher urinary volume, but also higher calcium, oxalate, and uric acid (each p < 0.01), while having lower calcium phosphate supersaturation (p < 0.037).
Conclusions: Kidney stone formers with elevated urinary ammonium levels have a unique clinical profile including a higher prevalence of recurrent urinary tract infections, history of bowel resection, and urinary tract reconstruction. Addressing the specific causes for elevated urinary ammonium in addition to optimizing urinary parameters may help direct preventative measures in this population.