Clinical studies on recurrence of urolithiasis. (2) Hypercalciuria and recurrence of urolithiasis

According to the dynamics of the urinary calcium excretion mechanism, we have classified the patients with urolithiasis into 4 groups, namely group I (normocalciuria; urinary calcium excretion of 270 mg/day or less for male patients and 210 mg/day or less for female patients), group II (absorptive hypercalciuria; hypercalciuric with urinary calcium excretion of 200 mg/day or less under the low calcium diet), group III (renal hypercalciuria; hypercalciuric with urinary calcium excretion exceeds 200 mg/day even under a low calcium diet), and group IV (hyperparathyroidism; hypercalciuric patients as in group III with high serum calcium). Of the 97 stone formers, 77 were classified into group I, 9 into group II, 8 into group III and 3 into group IV. Both under the restricted diet and under the ambulatory free diet, urinary calcium excretion of groups II, III and IV was significantly higher than that of the group I patients. It was noteworthy, however, that some of the patients in group I excreted much calcium without restriction of their diet. Although no difference in excretion of oxalate, magnesium and phosphate was observed between the 4 groups, the patients in groups II, and III excreted more uric acid into their urine than group I patients. As for stone recurrence rate, no difference was noted between group I and group II, III or IV. Based on these findings, we conclude that hypercalciuria has no significant role in the stone forming mechanism. However, lowering of urinary calcium and other stone forming constituents is mandatory in preventing stone recurrence until the mechanism of stone formation is elucidated more precisely.