Potassium Sensitivity Test Solution for Interstitial Cystitis
The Potassium Sensitivity Test (PST) should not be performed for diagnosing Interstitial Cystitis, as it lacks the specificity and sensitivity to change clinical decision-making and is not recommended by current guidelines. 1, 2
Why the PST is Not Recommended
The American Urological Association explicitly states that the potassium sensitivity test has neither the specificity nor sensitivity to change clinical decision-making in the diagnosis of IC/BPS. 1 This recommendation is reinforced by current diagnostic guidelines that emphasize the test should not be performed as part of the diagnostic workup. 2
Historical PST Solution Composition (For Reference Only)
While the test is not recommended, the historical literature describes two different potassium concentrations that were used:
Standard PST Protocol
- 0.4 M potassium chloride (KCl) solution was the traditional concentration used for the potassium sensitivity test 3, 4
- This concentration was instilled intravesically to assess bladder discomfort and identify increased urothelial permeability 5
Modified Lower-Concentration Protocol
- 0.2 M potassium chloride (KCl) solution was investigated as a less traumatic alternative 6, 5
- This lower concentration was compared against 0.9% normal saline (NaCl) during cystometry 6, 5
- The modified test assessed maximum bladder capacity (Cmax) with saline first, then with 0.2 M KCl 5
- A decrease in Cmax greater than 30% with the potassium solution was considered indicative of IC 5
Critical Clinical Pitfalls
The 0.4 M KCl concentration can be extremely painful for patients with IC, which led investigators to explore the less concentrated 0.2 M solution. 5 However, even with modified protocols showing sensitivity of 85.5% and specificity of 81.6%, neither test provides 100% diagnostic accuracy. 4
The test has poor specificity - positive results occur in 41% of patients with hypersensitive bladder, 22% with detrusor overactivity, and 18% with stress urinary incontinence who do not have IC. 4 This high false-positive rate makes it unreliable for clinical decision-making.
Current Recommended Diagnostic Approach
Instead of the PST, the diagnostic workup should include:
- Urinalysis and urine culture as mandatory laboratory tests 1, 2
- Urine cytology if the patient has a smoking history or unevaluated microhematuria 1, 2
- Baseline symptom documentation using validated tools such as the Interstitial Cystitis Symptom Index (ICSI) and Visual Analog Scale (VAS) 2
- Cystoscopy only when diagnosis is in doubt or when Hunner lesions are suspected, not for routine uncomplicated presentations 1, 2