Clinical study of ammonium acid urate urolithiasis

Ammonium acid urate (AAU) urolithiasis is a rare condition; however, it is endemic in some countries, with an especially high incidence in Asia. This study was conducted to investigate the special presentation of patients with AAU urolithiasis in Taiwan. Reports of 3457 stones were retrospectively reviewed from January 2005 to January 2010 and 25 patients with urinary stones (0.7%) containing AAU crystals were identified. The clinical and biochemical presentation of all stones were compared to evaluate the specific comorbidities of AAU stones. AAU stones were observed in 11 males (44%) and 14 females (56%) with a mean age of 60.60 ± 16.81 years and mean body mass index of 25.55 ± 3.73 kg/m(2). AAU stones were frequently observed in the bladder (44%) and they were significantly larger (mean size 1.90 cm) than the non-AAU stones (mean size 1.22 cm). Other significant comorbidities of AAU stones included chronic kidney disease (CKD) (60%), urinary tract infections (UTIs) (52%), irritable bowel syndrome (IBS) (36%), and gout (28%). In addition, there were also three patients with coexisting urothelial carcinoma (12%) in the AAU-stone group. Patients with AAU urolithiasis were predominantly female, older in age, had increased bladder presentation, larger stones and a high percentage of coexisting CKD, UTIs, IBS, gout, and even urothelial carcinoma. Therefore, it is important for clinicians to evaluate and protect renal function in patients with AAU urolithiasis.