According to MedlinePlus, the normal eosinophil count, or eos blood level, is less than 350 cells per microliter. The level is found by counting how many eosinophils are present per 100 cells in a blood sample. High levels can be caused by an allergic reaction like hay fever, a parasite or medicines, and a low count can be caused by alcohol intoxication or an overproduction of steroids in the body.
MedlinePlus states that eosinophil levels may vary slightly according to the laboratory, but a high count helps doctors determine if a patient has acute hypereosinophilic syndrome, Cushing’s disease, an allergic reaction caused by hay fever, asthma, autoimmune diseases, leukemia or a parasite infection such as worms. Medicines such as interferon, tranquilizers, certain antibiotics and laxatives and amphetamines can heighten eosinophil levels; it is important for the patient to notify doctors of any use of such products for precise diagnosis.
MedlinePlus notes that eosinophil blood levels are found by taking a blood sample and adding a stain so the eosinophils appear as orange-red granules. The technician then counts how many eosinophils become visible per 100 cells and multiplies the amount by the white blood cell count to get the absolute count.