Eosinophil cationic protein (ECP)
What it measures, and what changes the number.
Eosinophil cationic protein is a protein stored in the granules of eosinophils, a type of white blood cell involved in allergic reactions and defence against parasites. When eosinophils are activated they release ECP, so the test is used as a marker of eosinophil activity rather than eosinophil numbers. It is usually measured in serum.
ECP is often read alongside the eosinophil count, total IgE and allergy screening tests such as Phadiatop, because together they describe both how many eosinophils are present and how active they are.
Handling matters a great deal for this test. Eosinophils keep releasing ECP inside the tube while the blood clots, so labs standardise the clotting time and temperature before separating the serum, and results from different handling protocols or assays may not be comparable. Labs may print it as Proteína catiónica de eosinófilos.
Often read alongside: Eosinophils, Eosinophils %, IgE, Phadiatop (inhalant screen), White blood cells