ECP (Eosinophil Cationic Protein) Test — A Sensitive Biomarker for Eosinophil-Mediated Inflammation

Eosinophil Cationic Protein (ECP) is a positively charged protein released from eosinophil granules during activation.
Because eosinophil counts alone cannot fully reflect eosinophil activity, the ECP test provides valuable insight into the actual activation state of eosinophils, making it highly useful in allergic and eosinophilic inflammatory diseases.

---

1. Purpose of the ECP Test

ECP measurement is clinically useful in the following situations:

1) Assessing Activity of Allergic Diseases

• Asthma
• Allergic rhinitis
• Atopic dermatitis
• Food and drug allergy

ECP levels correlate with disease activity and help evaluate the degree of eosinophilic inflammation, especially in asthma.

2) Differentiating Eosinophil-Related Conditions

• Eosinophilia
• Eosinophilic gastrointestinal disorders (EGE, EoE)
• Parasitic infections

3) Monitoring Treatment Response

• Corticosteroids
• Antihistamines
• Biologic agents (anti-IL-5, anti-IgE, etc.)

A decrease in ECP after treatment indicates improvement in eosinophilic inflammation.

---

2. Testing Method — CLIA-Based Immunoassay

Most laboratories perform ECP quantification using:

CLIA (Chemiluminescent Immunoassay)

or

ECLIA (Electrochemiluminescent Immunoassay)

Principle:
Serum ECP binds to anti-ECP antibodies coated on microparticles. A labeled antibody then binds to the complex, producing a chemiluminescent signal proportional to the ECP concentration.

Advantages

• High sensitivity
• Excellent reproducibility
• Fully automated platforms available

Specimen: Serum

---

3. Reference Range

Values may differ by instrument and institution.

• Typical reference range: 0–24 ng/mL

Always refer to the laboratory’s specific reference interval.

---

4. Clinical Significance & Interpretation

ECP increases not simply with eosinophil count, but when eosinophils are activated.
Therefore, results should be interpreted together with the CBC eosinophil count.

---

✦ Conditions Associated with Elevated ECP

1) Asthma

• Particularly elevated in eosinophilic asthma
• Higher during exacerbations
• Decrease after treatment → good disease control

2) Atopic Dermatitis

• Frequently elevated in moderate to severe cases
• Correlates with clinical severity (e.g., SCORAD score)

3) Allergic Rhinitis

• Increased in both seasonal and perennial disease

4) Parasitic Infections

(Strongyloides, Ascaris, Toxocara, etc.)

5) Eosinophilia

Due to autoimmune disease, hematologic malignancies, or other systemic disorders

6) Eosinophilic Gastrointestinal Disorders

• Eosinophilic esophagitis (EoE)
• Eosinophilic gastroenteritis (EGE)

ECP elevation often reflects ongoing tissue-level inflammation.

---

✦ Conditions Associated with Decreased ECP

• Corticosteroid therapy
• Biologic therapy (anti-IgE, anti-IL-5, etc.)
• Well-controlled asthma or atopic disease

---

5. Important Considerations in Interpretation

1) High sensitivity, but limited specificity

ECP can rise in many allergic and inflammatory conditions, so it should not be used as a stand-alone diagnostic test.

2) Always interpret with the eosinophil count

• Normal eosinophils + elevated ECP: transient or early eosinophil activation
• High eosinophils + high ECP: strong indicator of active eosinophilic inflammation

3) Steroid therapy rapidly lowers ECP

• Useful for monitoring treatment effectiveness
• But timing of medication must be considered

4) Clinical context is essential

• Underlying allergic disease
• Recent exacerbation
• Medication history
• Travel or parasitic exposure

---

📚 References

• Venge P. Eosinophil cationic protein (ECP): its role in allergic inflammation. Clin Exp Allergy. 1990.
• Kariyawasam HH, Robinson DS. The role of eosinophils in asthma. Curr Opin Allergy Clin Immunol. 2007.
• Koller DY et al. Monitoring serum ECP in children with asthma. J Allergy Clin Immunol. 1995.
• Johansson SGO et al. Allergic diseases and eosinophil activation. Allergy. 2001.
• Rothenberg ME. Eosinophilic gastrointestinal disorders. J Allergy Clin Immunol. 2004.