Stone risk after bladder substitution with the ileal-urethral Kock reservoir

The study was carried out to compare urinary biochemical and physicochemical environments in patients who had undergone bladder substitution with the ileal-urethral Kock reservoir, and who had no actual urinary infection, with those of healthy subjects.

The participants were 23 male patients who had undergone bladder substitution with the ileal-urethral Kock reservoir and 25 healthy men. All subjects had sterile urine at the time of urine collection. Concentrations of calcium, magnesium, phosphorus, creatinine, citrate, oxalate, and ammonia in 24-h urine samples were measured. Estimates of ion activity products of calcium oxalate (CaOx), calcium phosphate (CaP), brushite (Bru), and magnesium ammonium phosphate (MAP) in urine were calculated according to Tiselius.

There was no significant difference in 24-h urinary volume between patients with a bladder substitute and the healthy controls. For most of the other measured values the results for patients differed significantly from those for controls. The most striking findings were markedly lower urinary excretion rates of citrate (p < 0.0001) and higher urine pH (p < 0.0001) in patients compared with controls. These findings were reflected in significantly higher levels of urinary supersaturation with respect to CaOx (p < 0.0001), CaP (p <0.0001), Bru (p < 0.0001) and MAP (stuvite) (p < 0.0001) in patients with a bladder substitute compared with healthy subjects.

Hypocitraturia seems to be the main risk factor for calcium stone formation in non-infected Kock reservoir patients, and citrate supplementation appears to be the most obvious choice for stone prophylaxis in patients with intestinal urinary diversion and recurrent renal stone formation.