LAUSR

OBJECTIVE To evaluate and profile ammonium acid urate (AAU) stone formers utilizing a large contemporary cohort. MATERIALS AND METHODS A retrospective review of all patients with documented AAU urolithiasis on stone analysis was performed from 1995 to 2013. A stone was considered AAU if it contained at least 10% of the total composition on stone analysis. RESULTS Of 12,421 stones, a total of 111 AAU stones were identified in 89 patients. Seventy-two patients (81%) had mixed composition stones. Of the 89 AAU patients, 10 (11%) had chronic kidney disease, 12 (13%) had recurrent urinary tract infections, 8 (9%) had diabetes mellitus, 25 (28%) had a history of ileostomy or bowel resection, and 11 (12%) had significant diarrhea or inflammatory bowel disease. Additionally, 20 (22%) had prior prostate surgery with bladder neck contracture and 8 (9%) were managed with a chronic indwelling catheter. Surgical intervention was required in 74 patients (83%). At the median follow-up of 4.9 years, 19 patients (21%) had stone recurrence with a median time to recurrence of 22 months (interquartile range: 10.5-42.0). CONCLUSION AAU stones are rare. In addition to previously described risk factors for AAU stone formation, patients with prior prostate surgery and bladder neck contracture or a surgically altered bladder may be at increased risk for formation. Furthermore, the long-term follow-up provided by this large AAU cohort demonstrates a significant risk for stone recurrence.