A new direct test of bladder permeability

Purpose: A proposed cause of interstitial cystitis is increased bladder permeability but to our knowledge this theory has not been proved by direct testing. We developed a safe, relatively painless, direct test of bladder permeability. Materials and Methods: The original permeability test involved placing 4% lactulose and 1% rhamnose intravesically, then drawing blood to assay for these sugars. Initial feasibility studies were performed in rabbits with bladder epithelium that was intact or disrupted by a 50% acetone rinse. In humans the initial goal was to distinguish intact bladders from those known to have increased permeability. Since distention is known to increase permeability temporarily, we studied patients with interstitial cystitis immediately after distention. Results: Neither sugar was absorbed from intact rabbit bladders, while each was absorbed from acetone rinsed bladders at 10, 20 and 30 minutes. We used 100 ml. of solution in the initial 8 humans, including 6 with interstitial cystitis and 2 controls. At 30 minutes each sugar was absorbed from interstitial cystitis bladders but neither was absorbed from intact bladders. The test solution was then changed to 5% rhamnose. Mean rhamnose absorption plus or minus standard deviation was much greater in the 6 patients with interstitial cystitis than in 8 controls (26.3 ± 26.1 versus 0.78 ± 0.87 nmol./ml, serum, p = 0.008). With 1 exception interstitial cystitis serum levels were at least 4-fold higher than the highest control level. Conclusions: This new permeability test clearly distinguishes intact versus distended bladders. It may be performed to test whether bladder permeability is increased in interstitial cystitis.