Diagnostic accuracy of serum proteinase 3 antineutrophil cytoplasmic antibodies in children with ulcerative colitis

Background and Aim Serologic markers such as myeloperoxidase (MPO) antineutrophil cytoplasmic antibodies (ANCA) (MPO‐ANCA) have been used to screen patients for ulcerative colitis (UC). However, MPO‐ANCA shows limited accuracy in Asians. Proteinase 3 ANCA (PR3‐ANCA) has performed better at UC diagnosis in Japanese adults than MPO‐ANCA. The present study aimed to evaluate usefulness of PR3‐ANCA for diagnosis of UC in Japanese pediatric practice. Methods Patients under 17 years old undergoing assessment at 12 Japanese pediatric centers between November 2016 and February 2018 were prospectively enrolled and divided into groups with UC, Crohn's disease (CD), intestinal disease control (IC), and healthy control (HC). Serum PR3‐ANCA and MPO‐ANCA were analyzed using chemiluminescence enzyme immunoassay kits. Results Sera from 367 patients (148 with UC at a median age of 12 years; 120 with CD, 13 years; 56 with IC, 10.5 years; and 43 with HC, 10 years) were examined. Median PR3‐ANCA values in UC (1.6 U/mL) were greater than in CD (0.2; P