Abnormal urinary potassium metabolism in patients with interstitial cystitis

If most patients with interstitial cystitis (IC) have epithelial leakage allowing urinary K to penetrate the interstitium and provoke symptoms, urinary K should be lower in untreated patients than in healthy subjects and it should increase with successful heparinoid treatment. This study tested these hypotheses.

Na, K and creatinine (Cr) were determined in spot urine samples from new, symptomatic, untreated patients with IC meeting all National Institute of Diabetes and Digestive and Kidney Diseases clinical diagnostic criteria, returning patients with IC reporting 50% or greater symptom improvement after 4 or greater months of oral heparinoid therapy and control subjects, and in 24-hour urine samples from new untreated patients and controls.

In spot urine specimens of 37 new patients with IC K-to-Cr ratios were significantly lower than in 18 controls (0.51 vs 0.88 mg/mg Cr, p = 0.001). A total of 50 successfully treated patients with IC had significantly higher K-to-Cr ratios than those in 37 new patients (0.66 vs 0.51 mg/mg Cr, p = 0.025). Na-to-Cr ratios in the 3 groups were not significantly different. In 24-hour urine specimens 30 new patients had lower average K (31.0 vs 46.2 mEq/l, p = 0.01) and lower K-to-Cr ratios (0.43 vs 0.52 mg K/mg Cr, p = 0.01) than in 47 controls, while Na was not significantly different.

Our finding of lower urinary K in new, untreated patients supports the concept of abnormal epithelial permeability and K absorption in IC. Higher urinary K in successfully treated vs untreated patients may reflect decreasing urinary K absorption due to mucosal repair and a resulting decrease in epithelial permeability. K/mg Cr appears accurate for normalizing urinary K.