Ammonium acid urate urolithiasis in Japan

Aim: Ammonium acid urate (AAU) calculi are a rare urolithiasis in developed countries but are endemic in developing countries. We assessed the features of AAU urolithiasis in Japanese patients. Methods: We reviewed hospital charts of patients with urolithiasis who were treated with extracorporeal shock wave lithotripsy and endourological procedures at Sagamidai Hospital (Kanagawa, Japan) from January 1992 to December 2001. On the basis of the results of stone analysis with an infrared spectrophotometer, AAU stones were found. Results: Of 8664 urolithiasis that we reviewed, 33 calculi (0.38%) from 29 patients contained AAU crystals. From crystallographic findings, we defined two types of AAU‐containing stones: pure and mixed AAU urolithiasis. Pure AAU urolithiasis were seen in 13 stones from 10 patients and mixed AAU in 20 stones from 19 patients. We found significant differences between the groups: the pure AAU group predominantly consisted of young, thin women and the mixed group consisted of middle‐aged men. Laboratory findings showed trends of low levels of serum protein, potassium, and urine pH in the pure AAU group. Conclusions: Because each type of AAU urolithiasis is associated with different patient characteristics and pathophysiological features, it is important to understand the type of AAU urolithiasis in patients with calculi.