[Clinical studies on the recurrence of urolithiasis (5). Diurnal variation in urinary pH and stone compositions].

Correlation of the composition of the urinary calculi with urine pH, especially of diurnal variation, and composition of urinary excretion was studied. Urine pH in the patients with uric acid stones was constantly low and urinary pH in the patients with apatite and struvite stones was always high. Diurnal variation was not observed. In patients with pure calcium oxalate stones, however, urinary pH was low in the early morning, increased during the daytime, and was lowered at night. In the patients with mixed calcium oxalate-phosphate stones, a similar diurnal variation in urinary pH was found, but the urinary pH in the early morning was significantly higher in the patients with mixed calcium oxalate-phosphate stones than in those with pure calcium oxalate stones. Urinary tract infection did not influence these differences in urinary pH. Urinary excretion of calcium in the patients with mixed calcium oxalate-phosphate stones was significantly higher than that in those with pure calcium oxalate stones. No other correlations were observed between composition of the urinary calculi and urinary excretion of calcium, oxalate, uric acid, phosphate or magnesium. From these findings we conclude that urinary pH and urinary calcium are the most important factors determining the composition of the urinary calculi.