Specific causes of a high white blood cell count include:

• Allergy, mainly bad allergic reactions
• Asthma
• Bacterial, viral, fungal or parasitic infections
• Burns
• EGPA (formerly Churg-Strauss syndrome)
• Medicines, such as corticosteroids and epinephrine
• Hay fever
• Leukemia
• Lymphoma
• Myelofibrosis
• Polycythemia vera
• Pregnancy
• Rheumatoid arthritis
• Sarcoidosis
• Smoking
• Tuberculosis
• Vasculitis
• Whooping cough

A high white blood cell count is a rise in the number of cells in the blood that fight infections.

What's thought of as high in a white blood cell count varies from one lab to another. This is because labs set their own reference ranges based on the people they serve. Most often, a count of more than 11,000 white blood cells in a microliter of blood is thought to be high for adults.

A high white blood cell count most often means one of the following has led to a rise in white blood cells:

• An infection.
• Reaction to a medicine.
• A bone marrow condition.
• An immune system issue.
• Sudden stress such as hard exercise.
• Smoking.

A test a healthcare professional orders to diagnose a condition can show a high white blood cell count. A high white blood cell count rarely is found by chance.

Talk to your healthcare professional about what your results mean. A high white blood cell count plus results from other tests might show the cause of your illness. Or you might need other tests for more information about your condition.