Definition of leukocytosis (high white blood cell count)
High white blood cell count is an increase in disease-fighting cells (leukocytes) circulating in your blood. High white blood cell count is also called leukocytosis.
The threshold for high white blood cell count varies from one medical practice to another. A count of more than 11,000 leukocytes in a microliter of blood in adults is generally considered a high white blood cell count. The threshold for a high white blood cell count in children varies with age and size.
Causes of leukocytosis (high white blood cell count)
A high white blood cell count usually indicates:
- An increased production of white blood cells to fight an infection
- A reaction to a drug that increases white blood cell production
- A disease of bone marrow, causing abnormally high production of white blood cells
- An immune system disorder that increases white blood cell production
Specific causes of high white blood cell count include:
- Acute lymphocytic leukemia
- Acute myelogenous leukemia (AML)
- Allergy, especially severe allergic reactions
- Chronic lymphocytic leukemia
- Chronic myelogenous leukemia
- Drugs, such as corticosteroids and epinephrine
- Certain bacterial infections
- Certain viral infections
- Polycythemia vera
- Rheumatoid arthritis
- Stress, such as severe emotional or physical stress
- Whooping cough
When to see a doctor
A high white blood cell count is usually found when your doctor has ordered 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 and results from other tests may already indicate the cause of your illness, or your doctor may suggest other tests to further evaluate your condition.