Comparative assessment of maximal bladder capacity, 0.9% NaCl versus 0.2 M KCl, for the diagnosis of interstitial cystitis:: A prospective controlled study

Purpose: Increased urothelial permeability has been proposed as a cause of interstitial cystitis (IC). The potassium sensitivity test assesses bladder discomfort after instillation of 0.4 M KCl for identification of increased urothelial permeability. Since exposure to 0.4 M KCl may be extremely painful for patients with IC we investigated a less traumatic alternative. Materials and Methods: The study comprised 38 controls and 40 patients with IC. In all subjects cystometry was performed with 0.9% NaCl followed by 0.2 M KCl, and filling volume at first urge and maximum bladder capacity (Cmax) were assessed for both solutions. Results: Controls did not show a significant change in Cmax. KCl decreased Cmax in 37 of 40 (92%) patients with IC with a mean decrease of 30%. The examination was painless in all controls and in 33 of 40 (82%) patients with IC, and was moderately painful in 7. Conclusions: For demonstration of increased potassium sensitivity and diagnosis of IC, comparative assessment of Cmax is a well tolerated alternative to the 0.4 M potassium sensitivity test. Statistical evaluation of these results suggests that a decrease in Cmax greater than 30% is indicative of IC.