Background: The prevalence of perinuclear antineutrophil cytoplasmic antibodies (p-ANCA) does not significantly vary in ethnically diverse populations. The prevalence of p-ANCA is high in ulcerative colitis and primary sclerosing cholangitis. While the prevalence of ulcerative colitis in Asian populations is low, it is interesting to know the prevalence of p-ANCA in such a population.
Methods: Sera from 33 cases of ulcerative colitis diagnosed during the last 10 years at the diarrhea clinic, Division of Gastroenterology, Siriraj Hospital, were prospectively compared with case controls consisting of 15 cases of diarrhea from non-inflammatory bowel diseases and 25 non-diarrheic patients. Indirect immunofluorescence assay was used to detect p-ANCA in all the sera.
Results: Positive p-ANCA tests were found in 13 of the 33 patients with ulcerative colitis and in one of the 40 controls. Sensitivity of the test was 39.4% and the specificity was 97.5%. The one patient with positive p-ANCA in the control group was the patient with irritable bowel syndrome. Of the 13 p-ANCA-positive ulcerative colitis patients, two cases were found to have proctosigmoiditis, seven cases had left-sided colitis, and four cases had pancolitis. Perinuclear antineutrophil cytoplasmic antibodies was one of the 22 cases of first-degree relatives of ulcerative colitis patients (22 relatives from 12 index ulcerative colitis cases). There was no correlation between the positivity of p-ANCA and disease activity, and extent of the disease.
Conclusion: The prevalence of p-ANCA in Thai patients with ulcerative colitis (39.4%) is lower than that in the Western population. Although the prevalence of p-ANCA is low in the Thai population, it should serve as a useful tool in diagnosing ulcerative colitis in this part of the world where the disease is uncommon and difficult to diagnose. The negativity of p-ANCA in almost all first-degree relatives of Thai ulcerative colitis patients should be further elucidated.