Quantifying eosinophil cationic protein with ImmunoCAP ECP results in proper evaluation of asthma patients

ImmunoCAP ECP measures the level of Eosinophil Cationic Protein (ECP) in serum. Eosinophils are the cells chiefly responsible for producing the inflammation associated with asthma. When eosinophils in the airway are activated, they undergo degranulation causing airway epithelial damage. This can lead to chronic inflammatory disease of the airway.

Asthmatic patients with eosinophilic inflammation have elevated levels of ECP in serum and other body fluids such as bronchial alveolar fluid and (induced) sputum. A high level of serum ECP indicates inflammation, which is a risk factor for asthmatic patients.

Asthma therapy consists of suppressing chronic and persistent airway inflammation. Measuring ECP in a serum sample is an objective and direct way of estimating the severity of the airway inflammation and following the course of the disease.

ECP serum measurements can be used:

  • For monitoring inflammation in asthma
  • For guiding corticosteroid treatment in asthma
  • To find non-compliant patients

Expected test values

Normal adult values show a geometric mean of 5.5 µg/l and a 95th percentile of 13.3 µg/l. Values over 15 µg/l should be considered elevated. However, patients should be their own control during treatment follow-up. 

Specimen collection and preparation

Parameters such as blood collection tube, coagulation time and temperature must be kept within specified limits since they affect the concentration of released ECP in serum samples. The clotting represents the first incubation in the assay in which the ECP measured is to be reproducibly released from the eosinophils which have been activated by the inflammation.

  1. Collect blood by venipuncture using Terumo Venosafe Serum-Gel tubes. It is important that the tube is completely filled. Contact Phadia AB if a serum collection tube other than Venosafe is to be used.
  2. After collection, gently invert the tube several times. Do not shake or vortex the tube.
  3. Release ECP by clotting for 60 to 120 minutes at room temperature 20-24 °C. The temperature must not vary more than ±1 °C between samplings to give comparable results.
  4. Centrifuge at 1000–1300xg for 10 minutes at room temperature.
  5. Decant serum into a new tube.
  6. Serum samples may be kept at room temperature for shipping purposes. Otherwise store at 2-8 °C if assayed within five days after collection or at –20 °C if assayed later.

Note!  Plasma and haemolysed serum can not be used.

Test principle

The technology is based on an extremely high total binding capacity, achieved through a high binding capacity per mg cellulose in combination with an optimal amount of cellulose in each solid phase. This ensures binding of all relevant antibodies, regardless of antibody affinity, still giving low non-specific binding.

The ImmunoCAP solid phase consists of a cellulose derivative enclosed in a capsule. The hydrophilic, highly branched polymer provides an ideal microenvironment for allergens, binding them irreversibly while maintaining their native structure.

The test is designed as a sandwich immunoassay. 

Anti ECP, covalently coupled to the solid phase, reacts with the ECP in the patient serum sample.
After washing, enzyme-labelled antibodies against ECP are added to form a complex.
After incubation, unbound enzyme-anti-ECP is washed away, and the bound complex is then incubated with a developing agent.
After stopping the reaction, the fluorescence of the eluate is measured. The fluorescence is directly proportional to the concentration of ECP in the serum sample.

Important note

As in all diagnostic testing, a definitive clinical diagnosis should not be based solely on the results of a single test method. A diagnosis should be made by the physician after evaluation of all clinical and laboratory findings.