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

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.

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%).

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.

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.