Optimizing a Point-of-Care Lateral Flow Assay for Measuring Eosinophil Peroxidase in the Esophageal String Test

Background: Eosinophilic esophagitis (EoE) is an increasingly prevalent allergic disease characterized by eosinophilic inflammation and symptoms of esophageal dysfunction. Diagnosis and monitoring require repeated, invasive endoscopic esophageal biopsies to assess levels of eosinophilic inflammation. Recently, the minimally invasive esophageal string test (EST) has been used collect protein in mucosal secretions as a surrogate for tissue biopsies in monitoring disease activity. From the string, assessment of the eosinophil-associated proteins major basic protein-1 (MBP-1) and eotaxin-3 (Eot3) is used to assess disease activity; however, this requires measurement in a reference laboratory, for which the turnaround time for results exceeds the time required for histopathologic assessment of endoscopic biopsies. In addition, MBP-1 and Eot3 are not markers unique to eosinophils. These obstacles can be overcome by targeting eosinophil peroxidase (EPX), an eosinophil-specific protein, using a rapid point-of-care test. Currently, EPX is measured by a labor-intensive enzyme-linked immunosorbent assay (ELISA), but we sought to optimize a rapid point-of-care test to measure EPX in EST segments. Methods: We extracted protein from residual EST segments and measured EPX levels by ELISA and a lateral flow assay (LFA). Results: EPX levels measured by LFA strongly correlated with those quantified by ELISA (rs = 0.90 {95% CI: 0.8283, 0.9466}). The EPX LFA is comparable to ELISA for measuring EPX levels in ESTs. Conclusions: The EPX LFA can provide a way to rapidly test EPX levels in ESTs in clinical settings and may serve as a valuable tool to facilitate diagnosis and monitoring of EoE.