Potassium Testing The PST will be performed with the patient blinded to the identity of the two solutions as previously reported.10-12. All patients and controls will receive the same information in advance of the test procedure: that two separate, unidentified solutions will be instilled in the bladder and that they will be asked to grade their reactions. In brief, 40 ml of water will be instilled into the patient's bladder for 5 minutes and any reactions of urgency or pain will be graded on a scale of 0-5 (Figure 1A). Then water will then be removed and 40 ml of a potassium solution (40 mEq KCl in 100 mL water) will be instilled and reactions similarly graded. After both solutions are instilled and removed, the patient will be asked whether one solution caused more urgency or more pain than the other. Any difference between solutions will then be graded as mild, moderate, or severe.