Interleukin-6, Histamine, and Methylhistamine As Diagnostic Markers for Interstitial Cystitis

Objectives: To examine the specificity and sensitivity of the inflammatory markers histamine, methylhistamine, and interleukin-6 (IL-6) in the urine of patients with interstitial cystitis compared with that in healthy controls.

Methods: A total of 40 women with interstitial cystitis and 29 healthy controls collected 24-hour urine samples. During the 24 hours before urine collection, all participants refrained from consuming foods and medications that could contain bioactive amines. Methylhistamine and histamine were measured using radioimmunoassay kits and were normalized to urinary creatinine levels; IL-6 was measured using enzyme-linked immunosorbent assay. The data were analyzed by t tests, logistic regression analysis, and receiver operating characteristics.

Results: IL-6 and histamine were significantly greater in the patients with interstitial cystitis than in the controls (P = 0.0003 and P = 0.038, respectively). The methylhistamine levels were also greater in the patients with interstitial cystitis than in the controls, but the results did not reach significance (P = 0.063). Using a combination of IL-6 and methylhistamine/creatinine, cutoff points were established. Using these cutoff points, the sensitivity was 70.0%, specificity 72.4%, positive predictive value 77.8%, and negative predictive value 63.6%.

Conclusions: All three markers--histamine, methylhistamine, and IL-6--were greater in the patients with interstitial cystitis than in the controls. A combination of methylhistamine and IL-6 could be used as a sensitive and specific marker for interstitial cystitis.