What is considered a high white cell count?

In adults, a white blood cell count of over 11,000 white blood cells per microliter of blood is typically considered high, although normal ranges vary from practice to practice, states Mayo Clinic. The normal range is 4,500-10,000 white blood cells per microliter, according to MedlinePlus.

Possible causes of a high white blood cell count include the body fighting off an infection, an immune system disorder that affects white blood cell production, a reaction to a drug that spurs white blood cell production and bone marrow disease, notes Mayo Clinic. Specific conditions include several types of leukemia, myelofibrosis, rheumatoid arthritis, and drug reactions to corticosteroids and epinephrine.