The intravesical potassium sensitivity test and urodynamics: Implications in a large cohort of patients with lower urinary tract symptoms

Purpose: Bladder outlet obstruction secondary to benign prostatic hyperplasia (BPH) is the most common diagnosis in older men with lower urinary tract symptoms. However, these symptoms also can occur with interstitial cystitis. We determine whether the potassium sensitivity test is useful for distinguishing BPH from possible intersitial cystitis in patients with lower urinary tract symptoms. We also test the hypothesis that patients with these symptoms who have a positive test will have urodynamic findings consistent with the diagnosis of interstitial cystitis. Materials and Methods: The potassium sensitivity test was performed in 526 (95%) males and 25 (5%) females with lower urinary tract symptoms undergoing urodynamic testing. Urodynamic parameters in the positive and negative potassium sensitivity test groups were compared. Results: Of the patients 16% (89 of 551) had a positive potassium sensitivity test. Compared with patients who had a negative test, those who had a positive test were younger (61 versus 64 years, p = 0.03), had urgency at significantly lower volumes (108 versus 182 cc, p <0.0001), lower bladder capacity (343 versus 436 cc, p <0.0001) and lower post-void residual (49 versus 95 cc, respectively, p <0.001), Urodynamic parameters in the 24% (6 of 25) of women who had a positive potassium sensitivity test were similar to those in men who also had a positive test. Conclusions: Urodynamic findings in patients with lower urinary tract symptoms who have a positive potassium sensitivity test are significantly different from those in patients who have a negative test, and are similar to those findings characteristic of interstitial cystitis. Interstitial cystitis should be considered in patients with lower urinary tract symptoms who have a positive test. The potassium sensitivity and urodynamic tests may be a useful combination for screening men with lower urinary tract symptoms to identify those symptoms that may be due to interstitial cystitis versus BPH.