Eosinophilia - Causes and Grading What is Eosinophilia? Eosinophilia refers to an increase in eosinophils (a type of white blood cell) in the blood. It is defined as having more than 500 eosinophils/µL of blood. Grading of Eosinophilia: Mild: 500 - 1,500 eosinophils/µL Moderate: 1,500 - 5,000 eosinophils/µL Severe: > 5,000 eosinophils/µL Mnemonic for Causes: A-B-C-D A - Allergy: The most common cause. Includes asthma, allergic rhinitis, and atopic dermatitis. B - Bugs: Refers to parasitic infect