["Fecal diversion is occasionally indicated in patients with advanced perianal or colorectal Crohn's disease (CD). Because CD may result from an aberrant immunologic response to bacteria within the gut lumen, fecal diversion should be effective in managing these complications. However, not all patients achieve a clinical response after fecal diversion. CD patients can be characterized by their antibody responses against Pseudomonas fluorescens (I2), E.coli outer membrane porin C (OmpC), oligomannan (anti-Saccharomyces cerevisiae antibodies [ASCA]), and antinuclear antigens (perinuclear antineutrophil cytoplasmic antibodies [pANCA]). This study examines the association between clinical features and seroreactivity to these microbial and auto-antigens in predicting a clinical response to fecal diversion.", 'Twenty-seven consecutive CD patients undergoing fecal diversion were included. Sera were drawn and tested for anti-I2, anti-OmpC, ASCA, and pANCA in a blinded fashion. Response was assessed using clinical parameters.', 'Seventeen (63%) patients underwent fecal diversion for medically resistant proctocolitis and 10 (37%) for severe perianal disease. Median follow-up was 41 months. Seventeen (63%) patients achieved a clinical response. No preoperative clinical or surgical factor predicted response to diversion. Clinical response after fecal diversion was seen in 15 of 16 (94%) patients who were I2 positive compared with only 2 of 11 (18%) patients who were I2 negative (P = 0.0001). Seroreactivity to OmpC, ASCA, or pANCA was not associated with a clinical response to diversion.'] Do antibodies to I2 predict clinical response to fecal diversion in Crohn 's disease?