Eosinophils are a type of white blood cell that play a key role in the immune system by helping to fight infections, particularly those caused by parasites, allergens, and certain bacteria or fungi. They are produced in the bone marrow and travel through the bloodstream to various tissues where they contribute to immune responses and inflammation
. An eosinophil count is a blood test that measures the number of eosinophils in the blood. This test is often part of a complete blood count (CBC) with differential, which evaluates the levels of different types of white blood cells. The absolute eosinophil count is calculated by multiplying the percentage of eosinophils by the total white blood cell count
. Normal eosinophil levels typically range from about 30 to 350 cells per microliter of blood, or less than 5% of the total white blood cell count. A count above 500 cells per microliter is considered eosinophilia, which means there are too many eosinophils in the blood. This condition can be caused by allergic diseases (such as asthma or eczema), parasitic infections, autoimmune diseases, certain cancers, reactions to medications, and other inflammatory conditions
. A low eosinophil count, called eosinopenia, can also occur and may be related to certain health conditions or medications
. In summary, the eosinophil count in a blood test helps doctors assess immune system activity and can aid in diagnosing allergies, infections, autoimmune disorders, and other medical conditions involving inflammation or abnormal immune responses
