CLINICAL AND BIOCHEMICAL FEATURES OF URIC-ACID NEPHROLITHIASIS

A clinical investigation was carried out on patients with uric acid st ones in order to study the frequency and pathogenesis of uric acid nep hrolithiasis. Of 652 patients with stones in the upper urinary tract i n whom the stone composition could be examined, 36 patients had uric a cid stones (5.5%). The male to female ratio was 11:1. The average age of the 33 male subjects was 49 +/- 11 years (mean +/- SD), and the 3 f emales were 22, 37 and 42 years old, respectively. Two of the females showed hypouricemia. With regard to stone composition, pure uric acid stones were present in 26 cases (72%), a mixed uric acid and calcium o xalate stones were found in 6 cases (17%), both pure uric acid and mix ed uric acid and calcium oxalate stones were observed in 3 cases (8%), and a mixed uric acid and sodium acid urate stone in 1 (3%). Biochemi cal studies on male patients showed that the blood uric acid level was higher in the uric acid stone group and the pure uric acid stone grou p compared to the calcium stone group. The blood uric acid levels of t he former 2 groups did not differ from the control group. With respect to urine chemistry, the excretion of calcium in the uric acid stone g roup was significantly lower than that in the control group. In the ur ic acid stone group and the pure uric acid stone group the excretion o f calcium tended to be lower than that in the calcium stone group. The amounts of oxalic acid excreted in the uric acid stone group and in t he pure uric acid stone group were low compared to the calcium stone g roup. Oxalic acid elimination in these 2 groups did not differ from th e control group. No difference was found in the excretion of uric acid among these groups. In the pure uric acid stone group the urinary pH in the early morning was 5.24 +/- 0.51 (n = 14), which was lower than the 6.07 +/- 0.74 (n = 24) found in the calcium stone group. The amoun t of uric acid excreted in 24-hour urine and the pH of the early morni ng urine in the patients with pure uric acid stones showed an inverse correlation (r = 0.46, n = 13). There were no significant differences in the fractional excretion of urate among the uric acid stone group, the pure uric acid stone group, and the calcium stone group, but it di d tend to be elevated in the latter group.