Menu Healthy Lifestyle Diseases & Conditions First Aid Symptoms Tests & Procedures Videos Definitions FAQs High white blood cell countUpdated: 2020-11-24DefinitionA high white blood cell count is an increase in disease-fighting cells in your blood. The exact threshold for a high white blood cell count varies from one laboratory to another. In general, for adults a count of more than 11,000 white blood cells (leukocytes) in a microliter of blood is considered a high white blood cell count. A high white blood cell count is also called leukocytosis.CausesA high white blood cell count usually indicates:An increased production of white blood cells to fight an infectionA reaction to a drug that increases white blood cell productionA disease of bone marrow, causing abnormally high production of white blood cellsAn immune system disorder that increases white blood cell productionSpecific causes of a high white blood cell count include:Acute lymphocytic leukemia Acute myelogenous leukemia (AML)Allergy, especially severe allergic reactionsChronic lymphocytic leukemia Chronic myelogenous leukemia Drugs, such as corticosteroids and epinephrineInfections, bacterial or viralMyelofibrosis (a bone marrow disorder)Polycythemia vera Rheumatoid arthritis (inflammatory joint disease)SmokingStress, such as severe emotional or physical stressTuberculosis Whooping cough When to see a doctorA high white blood cell count is usually found when your doctor orders tests to help diagnose a condition you're already experiencing. It's rarely an unexpected finding or simply discovered by chance. Talk to your doctor about what these results mean. A high white blood cell count, along with results from other tests, might already indicate the cause of your illness. Or your doctor may suggest other tests to further evaluate your condition. © 1998-2022 Mayo Foundation for Medical Education and Research(MFMER). All rights reserved. Terms of Use