# A197 ASSOCIATION BETWEEN ANTIMICROBIAL SEROLOGIES AND IBD LOCATION AND BEHAVIOUR: DATA FROM THE CIDSCANN INCEPTION COHORT

## TL;DR

This study examines how antimicrobial antibodies relate to Crohn's disease progression in children, finding that certain antibodies are linked to disease location and severity.

## Contribution

The study provides new insights into how antimicrobial serologies correlate with pediatric Crohn's disease progression and location.

## Key findings

- ASCA positivity is more common in patients with L1/L3 disease compared to L2 disease.
- CBir1 positivity is independently associated with progression to B2/B3 disease in Crohn's patients.
- ANCA positivity is higher in L2 disease compared to L1/L3 disease.

## Abstract

Antimicrobial serologies have been associated with Inflammatory Bowel Disease (IBD) type and Crohn’s disease (CD) progression. However, prospective pediatric data examining these associations while considering disease location are sparse.

1) Describe rates of serology positivity by disease location; 2) Assess the ability of serologies to predict CD progression to stricturing (B2) /penetrating (B3) behaviour, while accounting for IBD location.

Children with CD enrolled in the prospective multicentre Canadian Children IBD Network (CIDsCaNN) were included. ASCA IgA and IgG, CBir1, OmpC and ANCA positivity were measured centrally at Cedars-Sinai. We assessed variables at diagnosis and last follow up. We used Pearson’s Chi-Squared test to compare proportions and Mann-Whitney U test to compare medians between groups. We used multivariable Cox regression to determine the association between serologies and progression to B2/B3 amongst CD patients with B1 at diagnosis, while accounting for L1 location. We calculated area under the ROC curve (AUC) to quantify predictive ability.

There were 512 CD patients included: median age 13 y (IQR 10.8-14.9), follow up 3.3 y (IQR 1.9-5.0). There were 50/452 (11%) B1 CD patients who progressed (L1: 16/77 (21%); L2: 7/112 (6%); L3: 27/241 (11%)). ASCA+ was more frequent among patients with L1/L3 compared to L2 CD (28% vs 13%, p=0.009), while CBir1+ and OmpC+ rates did not differ by CD location (55% vs 48%, p=0.19 and 9% vs 9%, p=0.85). ANCA+ rate was higher among L2 CD compared to L1/L3 CD (30% vs 10%, p<0.001). In univariate survival analysis, CBir1+, ASCA+ and L1 were associated with progression to B2/B3 (Table 1). In multivariable analysis, only positivity for CBir1+ and L1 were associated with progression. CBir1 titre had only moderate ability to predict progression (AUC 0.65 (95%CI 0.57-0.72)).

While ASCA and CBir1 are associated with complicated CD in univariate analysis, this appears to be mediated by small bowel location for ASCA. While CBir1 was independently associated with B2/B3 disease, its predictive ability alone was limited.

Table 1. Unadjusted and Adjusted Hazard Ratios for Progression to B2 or B3 Complications

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