Metabolic factors in the causation of urinary tract stones in patients with enterocystoplasties

Stones are a common complication of the storage of urine in intestinal reservoirs. Previous studies have identified predisposing physical characteristics in the reservoirs. Biochemical and dietary factors have been little investigated. Fifteen patients (6 males and 9 females) who had undergone various enterocystoplasty operations and who had subsequently formed either upper or lower urinary tract stones were investigated. The programme has been previously described and included stone, blood and urine analysis and dietary review. Comparison was made with 15 age- and sex-matched idiopathic stone formers with normal bladders. Stones were infective in origin in 86% of cases, and 14% were sterile. Metabolic screen showed that 80% of enterocystoplasty patients had risk factors for at least three different types of stone. All patients had raised pH (mean 6.93) and hypocitraturia. Five had a raised alkaline phosphatase. Raised serum and urinary calcium, hyperoxaluria and hyperuricosuria were found in 33% of patients. Five had a 24-h urine volume below 1.6 l/day. All patients had a high risk index (P _SF) for phosphatic stones and 12 also for calcium oxalate stones. Compared to age-and sex-matched idiopathic stone-formers, the urine had a higher pH, sodium and protein excretion and a lower calcium and citrate excretion. Although the patients were already selected as stone-formers, the data show that metabolic and dietary factors are present. They may be as important in the aetiology of the stones, as the already recognised factors of infection and poor reservoir drainage. Investigation should include such factors, the presence of which may be taken into account in a prophylactic regime.