To describe the associations between elevated urinary ammonium and clinical characteristics of kidney stone formers. A 24-hour urine test is recommended in high-risk patients to identify urinary abnormalities and select interventions to reduce the recurrence risk. While elevations in urine ammonium may be seen in acidosis, diarrhea, high protein diets or due to pathogenic bacteria, the clinical characteristics of these patients has not been previously described.

We retrospectively identified adult patients with kidney stone disease who completed a 24-hour urine at our institution between 2006-2017. Patients with elevated urinary ammonium were identified (n=121) and matched 1:1 by age and sex to controls for an overall cohort of n = 242. Differences in medical and surgical history, 24-hour urine analytes and stone composition were compared.

Among 3,625 24-hour urine studies screened, 7.1% of patients showed high urinary ammonium. In our study cohort, patients with elevated urinary ammonium also showed higher urine volume, oxalate, calcium, uric acid, sodium, chloride and sulfate. Clinically, these patients had higher BMI, and more often had a history of recurrent urinary tract infections, diabetes, gout, bowel resection and urinary reconstruction history. Struvite stones tended to be more common in the elevated ammonium group versus control (n=7 vs 1, p=0.07).

Elevated urinary ammonium among kidney stone patients is relatively uncommon. However, these patients have higher rates of comorbid metabolic conditions, urinary tract infections, and bowel surgery. This finding should prompt further review of the patient's history and may help direct prevention strategies.

Urology. 2020 Jun 13 [Epub ahead of print]

Wilson Sui, Joel Hancock, John R Asplin, Edward R Gould, Ryan S Hsi

Department of Urology, Vanderbilt University Medical Center, Nashville TN., Litholink Corporation, Laboratory Corporation of America Holdings, Chicago, IL., Division of Nephrology, Department of Medicine, Vanderbilt University Medical Center, Nashville TN., Department of Urology, Vanderbilt University Medical Center, Nashville TN. Electronic address: .