# Poster Session II - A200 EVALUATION OF PERIPHERAL ABSOLUTE EOSINOPHIL COUNT AS A BIOMARKER OF DISEASE ACTIVITY IN EOSINOPHILIC ESOPHAGITIS

## TL;DR

This study explores whether blood eosinophil counts can track disease activity in eosinophilic esophagitis, potentially reducing the need for invasive endoscopies.

## Contribution

The study evaluates peripheral absolute eosinophil count as a non-invasive biomarker for monitoring eosinophilic esophagitis disease activity.

## Key findings

- Higher peripheral absolute eosinophil counts correlate with active histological disease in eosinophilic esophagitis.
- White exudate during endoscopy is associated with elevated peripheral absolute eosinophil counts.
- A threshold peripheral absolute eosinophil count of 0.15 x 109 cells/L distinguishes histological remission from active disease.

## Abstract

At present, the gold standard for eosinophilic esophagitis (EoE) diagnosis and monitoring is upper gastrointestinal endoscopy (EGD) and biopsy of the esophageal mucosa. Unfortunately, the need for multiple and/or sequential treatments in this population can lead to patients needing recurrent, invasive EGDs for evaluation of disease activity and treatment response over time.

To evaluate the association between peripheral absolute eosinophil count (pAEC) and esophageal eosinophilia as a tool for monitoring EoE disease activity without the need for EGD.

A cross-sectional study is ongoing in adult EoE patients seen at a tertiary care centre in London, Canada. Participants who underwent an EGD with esophageal biopsy and had an available pAEC are included. Demographic data, pAEC, histological disease activity, and endoscopic findings were collected from each EGD encounter. Participants were evaluated for the association between 1) histological disease remission (<15 eosinophils per high powered field averaged between mid and distal esophageal biopsies), 2) individual EGD findings and pAEC respectively. The relationship between pAEC and mean esophageal eosinophilia was assessed using correlation analyses. A receiver operator characteristic (ROC) analysis was used to identify a threshold pAEC associated with histological disease activity or EGD findings, where significant.

To date, 94 participants with 142 EGD encounters are included in the preliminary analyses. The median pAEC was higher in participants with active EoE on histology (0.3 x109 cells/L, interquartile range, IQR=0.6x109 cells/L) versus those in remission (0.2 x109 cells/L, interquartile range, IQR=0.6x109 cells/L, p = 0.0095). The median pAEC was higher in participants with white exudate on EGD (0.4 x109 cells/L, interquartile range, IQR=0.3x109 cells/L) versus those without (0.3 x109 cells/L, interquartile range, IQR=0.3x109 cells/L, p = 0.01). Additionally, the mean esophageal eosinophil count was positively correlated with pAEC (r = 0.24, p = 0.0026). A threshold pAEC=0.15 x 109 cells/L separated those with histological disease remission from those without (area under the curve, AUC=0.63, 95% confidence interval, CI = 0.53-0.74, p = 0.015). A threshold pAEC=0.37 x 109 cells/L separated those with white exudate on EGD from those without (AUC=0.73, 95%CI=0.59-0.87, p = 0.013).

To date, pAEC is positively correlated with histological disease activity in EoE, with higher pAEC associated with the presence of esophageal eosinophilia. Additionally, we see white exudate on EGD is associated with higher pAEC. With completion of this study, we hope to determine if pAEC is a simple and clinically-actionable biomarker of EoE disease activity. This may reduce the need for repeated, invasive endoscopies in an otherwise healthy population.

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