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 hyperplas ia (BPH) is the most common diagnosis in older men with lower urinary tract symptoms. However, these symptoms also can occur with interstitial cystiti s. We determine whether the potassium sensitivity test is useful for distin guishing BPH from possible intersitial cystitis in patients with lower urin ary tract symptoms. We also test the hypothesis that patients with these sy mptoms who have a positive test will have urodynamic findings consistent wi th 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 undergoin g urodynamic testing. Urodynamic parameters in the positive and negative po tassium sensitivity test groups were compared. Results: Of the patients 16% (89 of 551) had a positive potassium sensitivi ty test. Compared with patients who had a negative test, those who had a po sitive test were younger (61 versus 64 years, p = 0.03), had urgency at sig nificantly lower volumes (108 versus 182 cc, p <0.0001), lower bladder capa city (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 tho se in men who also had a positive test. Conclusions: Urodynamic findings in patients with lower urinary tract sympt oms who have a positive potassium sensitivity test are significantly differ ent from those in patients who have a negative test, and are similar to tho se 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 u seful combination for screening men with lower urinary tract symptoms to id entify those symptoms that may be due to interstitial cystitis versus BPH.