Eosinophil Cationic Protein (ECP)

The Eosinophil Cationic Protein (ECP) test is used to aid diagnosis, grade severity, and monitor bronchial asthma, atopic dermatitis, allergic rhinitis, food allergy, and related allergic diseases. It may support evaluation when a helminthic infection is suspected. Serial ECP measurement can be trended to assess response to anti-inflammatory treatment and to guide inhaled corticosteroid titration in asthma.

Eosinophil cationic protein is a ribonuclease contained within eosinophil granules and released after IgE-mediated or other forms of activation. ECP is cytotoxic to epithelial cells, mast cells, smooth muscle cells, and fibroblasts, and it modulates immunity in a manner that favors a Th2-predominant response. Because eosinophils are resident in mucosal tissues of the respiratory and gastrointestinal tracts and in many parenchymal organs, ECP release is linked to a broad range of clinical manifestations. Serum ECP rises with allergen exposure and correlates with eosinophil burden and with airway mucosal inflammation in asthma, although it does not correlate with bronchial hyperreactivity. Higher concentrations occur in invasive helminth infections and during flares of atopic dermatitis; the highest values are observed in hypereosinophilic syndrome. Elevated ECP is not specific for allergy and can be seen in bacterial sinusitis, certain renal neoplasms, and respiratory syncytial virus infection. Drug reaction with eosinophilia and systemic symptoms (DRESS) is associated with marked ECP elevation. Interpretation should be integrated with clinical findings and other laboratory data, including allergen testing when indicated.