“…Although the levels of PR3-ANCA in UC are lower than those in AAV ( 13 ), serum PR3-ANCA, which is more prevalent in UC than in CD, has emerged as a potential marker for accurately discriminating UC from CD ( 11 ), particularly when detection is performed using chemiluminescent immunoassays with an appropriate cut-off value ( 14 ). Furthermore, PR3-ANCA positivity can serve as a marker of disease activity and correlates with nonresponse to steroid therapy in moderate-to-severe UC and with primary nonresponse to antitumor necrotizing factor-α agents ( 3 , 15 ). In our patient with nonvasculitic UC, PR3-ANCA with the highest titer of 30-fold the cut-off value was present in serum (measured through fluorescence enzyme immunoassay [FEIA], Phadia® 250, Thermo Fisher Scientific Inc., Waltham, MA, USA), and PR3 antigen was detected in situ in the inflamed bowels (measured through immunohistochemical staining labeled with rabbit monoclonal anti-PR3 antibody [EPR6277] (ab133613, abcam®, Cambridge, UK) to human PR3 at 1/100 dilution in formalin-fixed paraffin-embedded sections according to the user instruction).…”