What is an EOS Blood Test?

EOS or eosinophil is a type of white blood cell that helps your immune system. These white blood cells increase when you have allergies, parasite infections, asthma, and reactions to drugs such as inflammation. Eosinophils represent only a small percentage of the total cell population in your body but they are important indicators in determining if you are battling any of the diseases mentioned above or to diagnose other medical conditions like early stage Cushing's disease or acute hypereosinophilic syndrome.

Normally, blood test like CBC or complete blood count will include information about the amount of eosinophils in your blood. In particular, a complete blood count includes a WBC (white blood cell) differential. The WBC differential checks the different types of white blood cells including eosonophil, neutrophils, lymphocytes, monocytes, and basophils. The functions of the other wbc's differ from each other but their common function is to protect the body from infections. The results of a WBC differential will indicate the presence (in percentage) of the five different types of white blood cells, whether each type has increased or not.

Another blood test that involves identifying eosinophils is the Absolute Eosinophil Count. Similar to the CBC, a blood sample will be taken from you and tested. The presence of eosinophil is determined using a stain called eosin. Under a microscope, a blood smear is stained with eosin (a red dye) and the technician counts the number of eosinophils for every 100 cells.

The absolute eosinophil count is computed by multiplying the eosinophil count and the total white blood cell count. This specific test is not normally done or requested by your health provider primarily because it is very specific to eosinophil. However, if a previous blood test result showed certain abnormalities and your health provider suspects the possibility of a certain diseases, he may ask you to undergo an absolute eosinophil count. The Absolute eosinophil count, for example, helps diagnose the early stages of Cushing's disease and acute hypereosinophilic syndrome.