Comparison of biochemistry and diet in patients with enterocystoplasty who do and do not form stones.

OBJECTIVE

To evaluate patients with a history of urinary stones in intestinal reservoirs and compare them with similar patients who have never formed stones.

PATIENTS AND METHODS

One consequence of storing urine in an intestinal reservoir is urolithiasis, and there are several theories on its cause, all based on limited evidence. There are many factors predisposing to stone formation, and dietary and biochemical factors might be useful to distinguish those who form stones from those who do not. In a prospective study (with ethical committee approval) we identified 15 patients (six male and six female, mean age 29 years) who had formed stones after an enterocystoplasty (group 1), and another 10 (three male and seven female, mean age 44 years) with no history of urolithiasis after enterocystoplasty (group 2). The respective mean (range) follow-up was 14.6 (8-24) and 15.2 (6-23) years. They were investigated using our stone-screening protocol described previously and the results compared between the groups using an unpaired Student's t-test, with statistically significance indicated at P < 0.05.

RESULTS

There was a statistically significant difference in almost all the variables assessed. The mean 24-h urine output was 41% higher (P = 0.009) and the mean citrate excretion 173% higher (P = 0.002) in group 2. The mean (range) urinary pH was 6.46 (6.0-7.0) and 6.93 (6.3-7.8) in groups 2 and 1, respectively (P = 0.005). Of the stone-forming elements, only the excretion of calcium was significant (2.78 vs 5.2 mmol/day, P < 0.001). The biochemical risk of stone formation was significantly higher for both calcium oxalate and calcium phosphate stones in group 1 than group 2 (P < 0.001 in both). From the dietary diaries there was a 24% higher fluid intake in group 2 (P = 0.04). The difference between group 2 and group 1 for the intake of magnesium (18.2 vs 12.38 mmol/day) and phosphate (49 vs 37.8 mmol/day) was statistically significant (P = 0.04 and 0.02, respectively).

CONCLUSIONS

Apparently the use of bowel in the urinary tract does not alone increase the risk of urolithiasis. Patients in group 1 were more prone due to the constituents of urine and possibly their dietary habits. This implies that with adequate fluid intake and eating a healthy balanced diet, the risk of urolithiasis can be reduced in patients with enterocystoplasty, as with idiopathic stone formers.