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

1. An infection
2. Reaction to a medicine
3. A bone marrow condition
4. An immune system issue
5. Sudden stress such as hard exercise
6. Smoking

Specific causes of a high white blood cell count include:

1. Allergy, mainly bad allergic reactions
2. Asthma
3. Bacterial, viral, fungal or parasitic infections
4. Burns
5. Churg-Strauss syndrome
6. Medicines, such as corticosteroids and epinephrine
7. Hay fever
8. Leukemia
9. Lymphoma
10. Myelofibrosis
11. Polycythemia vera
12. Pregnancy
13. Rheumatoid arthritis
14. Sarcoidosis
15. Smoking
16. Tuberculosis
17. Vasculitis
18. Whooping cough