PREVALENCE AND DIAGNOSTIC ROLE OF ANTINEUTROPHIL CYTOPLASMIC ANTIBODIES IN INFLAMMATORY BOWEL-DISEASE

Background: Antineutrophil cytoplasmic antibodies (ANCA) are of proven diagnostic value in a variety of vasculitides, where they are also th ought to play a pathogenic role. ANCA has also been detected in the se rum of patients with idiopathic inflammatory bowel disease (IBD), both ulcerative colitis (UC) and Crohn's disease (CD), and primary scleros ing cholangitis (PSC) with or without concomitant IBD. Although the pr evalence in PSC and UC is reported to be up to 85%, a much lower preva lence of around 10-20% has been reported in CD. Aim: To determine ANCA prevalence in a group of British patients with IBD and evaluate their use as a serological marker to distinguish between UC and CD. Methods : A total of 99 UC-only patients (44 males, median age 50) and 41 CD p atients (11 males, median age 47) were tested for ANCA using an alkali ne phosphatase technique at a 1:5 serum dilution. Controls were other diarrhoeal diseases including 17 coeliac disease (4 males, median age 41), 23 irritable bowel syndrome (5 males, median age 42), 5 infectiou s colitis (2 male, median age 64) and 36 healthy volunteers (13 males, median age 43). Results: ANCA was detected in 42/99 (42.4%) UC patien ts but in only 2/41 (5%) CD (P<0.0001). All ANCA were perinuclear in d istribution. No ANCA was detected in the control sera. The sensitivity of the test for the diagnosis of UC was 42% with a specificity of 98% . In patients with UC, no association was found between presence of AN CA and age, sex, disease extent, treatment or activity. However, ANCA- positive UC patients had longer median duration of disease (50 months vs. 29 months, P=0.031). Both CD ANCA-positive patients had colonic in volvement, but one also had ileal disease. Both had inactive disease a nd one was on mesalazine. Conclusions: ANCA is highly specific for UC and may be a helpful diagnostic test in distinguishing UC from CD and other diarrhoeal illnesses. Although ANCA positivity may reflect disea se heterogeneity within UC, no association with clinical features or t reatment of UC was demonstrated and it is therefore unlikely to play a pathogenic role. The correlation with disease duration needs further investigation.