Objectives To study the relationship between urinary tract infection, urine composition and concrement formation in patients with continent ileal reservoirs for urinary diversion. Patients and methods The study comprised 27 patients (seven men and 20 women, mean age 47 years, range 23–76) with continent ileal reservoirs who were followed for a mean of 67 months (range 13–146) by annual reservoiroscopy, intravenous urography and urine culture; at the final follow‐up, a sample of their morning urine was analysed for a range of compounds and the number and size of any particles present or produced in response to incubation with urease. Results The presence of urease‐producing bacteria was associated with the formation of concrement. However, a few patients in whom an infection with urease‐producing organisms was not detected also formed concrement. Urine from those patients forming stones tended to have a high calcium and a low citrate concentration. After incubation with urease, significantly more and larger particles were formed in the urine from stone formers. There was a strong correlation (r=0.8) between urinary calcium content and urinary pH when the urease‐induced precipitation commenced, and between urinary calcium and the size and volume of the crystals developed (r=0.9) after 4 h of incubation. Conclusions There are many factors which might influence the formation of concrement, e.g. outflow conditions, the presence of staples or infection in the reservoir, and the composition of the urine is also important. It thus appears appropriate to determine if measures to reduce urinary calcium and increase urinary citrate can decrease the episodes of stone formation in those patients with continent ileal reservoirs for urinary diversion who frequently form stones.

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