The effect of saline bladder washings on calcium oxalate crystal growth and aggregation.

Saline bladder washouts were obtained from 31 normal patients undergoing routine cystoscopy. A urine control was prepared by diluting a urine sample to the same creatinine concentration as the bladder washout. The inhibitory activities of the samples were then measured in a calcium oxalate seeded crystallization system. Washouts from the first 9 patients inhibited crystal aggregation more strongly than did the controls. This was attributable to microscopic blood contamination, since in the following 22 subjects, in whom contamination was excluded by the use of sensitive haemoglobin test strips, no increase in inhibition of aggregation was seen. The inhibition of calcium oxalate crystal growth by the washouts was consistently greater than that by the urine controls (p less than 0.05). This suggests that the bladder mucosa is a source of inhibitor(s) of crystal growth but not crystal aggregation.