Bladder management and risk of bladder stone formation in spinal cord injured patients.

PURPOSE We determined by statistical analysis whether method of management is associated with risk of bladder stone formation in spinal cord injured patients. MATERIALS AND METHODS A retrospective cohort study was performed of 457 patients admitted to Stoke Mandeville Hospital Spinal Injuries Center between 1985 and 1990 with more than 6 months of followup. Analysis included Cox regression and Poisson regression. RESULTS Relative to those patients treated with intermittent self-catheterization, the hazard ratio was 10.5 (p <0.0005, 95% confidence interval 4.0-27.5) for patients with suprapubic catheters and it was 12.8 (p <0.0005, 95% confidence interval 5.1-31.9) for those with indwelling urethral catheters. The absolute annual risk of stone formation in patients with a catheter was 4% compared with 0.2% for those on intermittent self-catheterization. However, having formed a stone, the risk of forming a subsequent stone quadrupled to 16% per year. Bladder stones were no more likely to form in patients with suprapubic catheters compared to those with indwelling urethral catheters (hazard ratio 1.2, p = 0.6). CONCLUSIONS In spinal cord injured patients long-term catheterization is associated with a substantial increased risk of bladder stone formation. This increased risk occurs independently of age, sex and injury level. Degree of injury (complete or incomplete) was considered in the model. Catheter type (suprapubic or urethral) did not change this risk significantly if at all.