Anti-neutrophil cytoplasmic antibody (ANCA) against proteinase 3 (PR3) is a marker for granulomatosis with polyangiitis, although it is also observed in people with inflammatory bowel disease (IBD), most notably ulcerative colitis (UC). For a study, researchers sought to examine ANCA and PR3-ANCA in children with IBD. They looked for anti-Saccharomyces cerevisiae antibodies (ASCA), ANCA (indirect immunofluorescence, IIF), and PR3-ANCA in 326 juvenile IBD patients and 164 controls (chemiluminescence immunoassay). For juvenile IBD, they used the Paris classification and observed liver symptoms such as primary sclerosing cholangitis (PSC) and autoimmune hepatitis (AIH).

PR3-ANCA was detected in 49/121 (40%) of UC, 20/187 (11%) of Crohn’s disease (CD), and 2/18 (11%) of IBD-unclassified (IBD-U) patients, but not in any of the controls. ANCA was found in 54% of UC patients and 12% of CD patients (IIF). Patients with PR3-ANCA positive UC had the more extensive disease (P=.070). Anti-PR3 ANCA was found in 14 of 21 (67%) UC patients with backwash ileitis (P=.011). In 19 UC and 3 IBD-U patients, they found PSC or PSC/AIH. Anti-PR3-ANCA positivity was seen in 15 of 22 (68%) patients with PSC or PSC/AIH, compared to 36 of 117 (32%) patients without PSC (P =.001). Patients with PR3-ANCA had increased levels of the gamma-glutamyl transferase, alanine transaminase, and aspartate transferase (P< 0.001, 0.001, and 0.006, respectively). ASCA-IgA positivity was found in 47% of CD patients and 6% of UC patients. There were no significant differences between PR3-ANCA-positive and -negative individuals in terms of age at diagnosis, disease activity, treatment requirement, or the number of hospitalizations. The findings supported the use of PR3-ANCA as a possible serological marker for pediatric UC and PSC.