An assessment of the use of intravesical potassium in the diagnosis of interstitial cystitis.

PURPOSE

We evaluated the use of intravesical potassium in the diagnosis of interstitial cystitis.

MATERIALS AND METHODS

A blinded test assessment on 39 consecutive subjects attending our urology clinic for the evaluation of symptoms consistent with interstitial cystitis was performed. The pain response to intravesical potassium and water as a control was measured. The response rate was compared to the results of cystoscopy using standard outcome measures associated with diagnostic test assessment.

RESULTS

The probability of having interstitial cystitis given a positive intravesical potassium test was 66%. This finding added no new useful information and would not be helpful with clinical decisions as the probability of having interstitial cystitis in this population was already 56% before the test. Similarly, if the test was negative then 46% or nearly half of the subjects were still likely to have interstitial cystitis. Therefore, a negative test would have no ability to rule out disease nor would it be useful in making clinical decisions about how to proceed with evaluation or therapy. Test characteristics were considered poor with a sensitivity of 69.5% and a specificity of 50%. Likelihood ratios (positive 1.39, negative 0.61) also indicated poor inclusion and exclusion capabilities.

CONCLUSIONS

The general use of intravesical potassium as a diagnostic test for interstitial cystitis is not validated. The diagnosis of interstitial cystitis must depend on the clinical presentation and endoscopic findings based on National Institutes of Health criteria.