[Clinical studies of the recurrence of urolithiasis (4). Crystal formation in urine and stone recurrence].

Relationship between stone formation and crystal formation in urine was studied. Crystals in the sediments of early morning urine in 238 stone formers and the same numbers of non-stone formers were examined by light microscopy. Almost all crystals found in the early morning urine were composed of calcium oxalate both in stone formers and in non-stone formers. The frequency of calcium oxalate crystal formation was slightly higher in stone formers than in non-stone formers, but, no significant difference was noted. On the other hand, the urine containing calcium oxalate crystals of the stone formers had significantly lower specific gravity than that of the non-stone formers. Calcium oxalate crystals in the urine were formed significantly more frequently in the recurrent or bilateral male stone formers than in male unilateral stone formers without previous stone history. Frequency of calcium oxalate crystal formation was not influenced by urinary excretion of calcium, oxalate, uric acid, phosphate and magnesium. These finding led us to the conclusion that it was clinically useful to measure urinary specific gravity in which calcium oxalate crystals were formed in predicting the risk of stone formation.