An eosinophil peroxidase activity assay accurately predicts eosinophilic chronic rhinosinusitis

Abstract

Background: A definitive diagnosis of eosinophilic chronic rhinosinusitis (eCRS) requires invasive surgical tissue sampling and histologic enumeration of intact eosinophils. Eosinophil peroxidase (EPX) is an accurate biomarker of sinonasal tissue eosinophilia in CRS regardless of polyp status. A less invasive and rapid method that accurately identifies tissue eosinophilia would be of great benefit to patients.

Objective: We sought to evaluate a new clinical tool that uses a nasal swab and colorimetric EPX activity assay to predict a diagnosis of eCRS.

Methods: A prospective, observational cohort study was conducted using nasal swabs and sinonasal tissue biopsies obtained from patients with CRS electing endoscopic sinus surgery. Patients were classified as non-eCRS (n = 19) and eCRS (n = 35) on the basis of pathologically determined eosinophil counts of less than 10 or greater than or equal to 10 eosinophils/HPF, respectively. Swab-deposited EPX activity was measured and compared with tissue eosinophil counts, EPX levels, and CRS-specific disease metrics.

Results: EPX activity was significantly increased in patients with eCRS than in patients without eCRS (P < .0001). With a relative absorbance unit cutoff value of greater than or equal to 0.80, the assay demonstrated high sensitivity (85.7%) and moderate specificity (79.0%) for confirming eCRS. Spearman correlations between EPX activity and tissue eosinophil counts (r_s = 0.424), EPX levels (r_s = 0.503), and Lund-Kennedy endoscopy scores (r_s = 0.440) in eCRS were significant (P < .05).

Conclusions: This investigation evaluates a nasal swab sampling method and EPX activity assay that accurately confirms eCRS. This method could potentially address the unmet need to identify sinonasal tissue eosinophilia at the point-of-care, as well as to longitudinally monitor eosinophil activity and treatment response.

Keywords: Eosinophilic chronic rhinosinusitis; eosinophil peroxidase activity; ethmoid biopsy; nasal polyps; tissue eosinophilia.

Figure 1.

Step-wise illustration of a new sinonasal swab sampling method and eosinophil peroxidase (EPX) activity assay for the reliable and accurate prediction of eosinophilic chronic rhinosinusitis (eCRS). Min: minutes; nm: nanometer; R. A. U. [492]: relative absorbance units at 492 nm.

Figure 2.

Eosinophil peroxidase (EPX) activity and intact eosinophil counts are significantly elevated in patients with eCRS compared to in non-eCRS. (A) Measured EPX activity values using middle meatal nasal swabs and corresponding ethmoid biopsy eosinophil counts in eCRS and in non-eCRS with respect to CRS endotype and phenotype. (B) EPX activity is significantly increased in eCRS compared to in non-eCRS (p<0.0001). (C) EPX protein levels in ethmoid and nasal polyp tissues are significantly elevated in eCRS compared to in non-eCRS (ethmoid) (p<0.05). (D) Eosinophil counts in ethmoid and nasal polyp tissue biopsies are significantly increased in eCRS compared to in non-eCRS (ethmoid) (p<0.0001). Data are represented as individual values ± the mean and standard deviation for each cohort. Individual data points in C and D are color coded to demonstrate matched pairs. CRSsNP: chronic rhinosinusitis without nasal polyps; CRSwNP: chronic rhinosinusitis with nasal polyps; eCRS: eosinophilic chronic rhinosinusitis; Eo/HPF: eosinophil per high-power field; EPX: eosinophil peroxidase; NS: not significant; R. A. U. 492: relative absorbance units measured at 492 nm.

Figure 3.

The sinonasal swab method and EPX activity assay is accurate at distinguishing eCRS from non-eCRS, demonstrated with the receiver operator characteristic area under the curve of 0.863 (p<0.0001).