The potassium sensitivity test: a predictor of treatment response in interstitial cystitis

OBJECTIVE: To determine whether the potassium sensitivity test (PST) can be used to predict the response to treatment with intravesical sodium hyaluronate in patients with interstitial cystitis. PATIENTS AND METHODS: Thirty-eight patients diagnosed with interstitial cystitis were recruited; each had a PST, carried out in a double-blind fashion, followed by six weekly doses of intravesical sodium hyaluronate. The patients were assessed before and after treatment using a self-administered interstitial cystitis symptom index (CSI) and problem index (PI). The clinical response was defined as none (<25% improvement in clinical symptoms), mild (>25%), moderate (50-75%) and excellent (>75%). RESULTS: The PST was positive in 23 and negative or indeterminate in 13 patients; two patients withdrew from the study. Overall 20 of 36 (55%) patients reported an improvement after six doses of intravesical sodium hyaluronate, but 17 (74%) with a positive PST improved, compared to only five (22%) with a negative test (P = 0.03). There was an improvement in the CSI after treatment in both groups, but a significant improvement in the PI only in patients with a positive PST (P = 0.01). The magnitude of change for the CSI and PI was significantly greater in the positive than in the negative group (CSI, P = 0.043; PI, P < 0.001). There were no major complications. Three patients complained of pain after the test, and two with a positive and one with a negative PST developed a urinary tract infection. CONCLUSIONS: Although the role of the PST in the diagnosis of interstitial cystitis requires further clarification, the test helps to predict the response to treatment with glycosaminoglycan-substitution therapy.