Evaluation of an automated assay for eosinophil-derived neurotoxin in serum

Eosinophil-derived neurotoxin (EDN) is a promising biomarker for eosinophil activation during inflammatory responses. Here we evaluate the analytical performance of an automated fluorescence enzyme immunoassay for EDN in serum and explore its relationship with eosinophil counts in both healthy participants and those with eosinophilic conditions.

Paired serum samples were collected from individuals for whom a complete blood count with differential was ordered. EDN was measured using the ImmunoCAP EDN Assay Kit (research use only, Phadia AB / provided by Thermo Fisher Scientific) and 40 samples were also measured using an ELISA kit (research use only, ALPCO).

The analytical measurement range of the ImmunoCAP assay was 2.6-200 µg/L. The imprecision across different EDN concentrations was ≤ 7.0 %. Stability and preanalytical requirements were determined. To minimize ex vivo degranulation and false elevation of EDN levels, serum should be removed from the cell pellet immediately after centrifugation. There was strong correlation for EDN measurements between ImmunoCAP and the comparative ELISA (r = 0.974), although a significant bias was observed. A 95th percentile reference range in 180 presumed healthy adults was calculated at 101 µg/L. Overall EDN was significantly higher in serum from patients with elevated circulating eosinophil counts (median = 120.0; P < 0.0001). However, individual patients may present with discordant presentation of eosinophil counts and EDN concentration.

Together these results demonstrate that the ImmunoCAP EDN Assay Kit can reliably measure EDN in serum and may be useful for the evaluation of patients with conditions associated with hypereosinophilia.