A 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.

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 a 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
• Infections, bacterial or viral
• Myelofibrosis (a bone marrow disorder)
• Polycythemia vera
• Rheumatoid arthritis (inflammatory joint disease)
• Smoking
• Stress, such as severe emotional or physical stress
• Tuberculosis
• Whooping cough

A 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.