What is the normal adult white blood cell (WBC) count range?

• A. Approximately 1,000 to 2,000 cells per microliter
• B. Approximately 4,000 to 11,000 cells per microliter
• C. Approximately 20,000 to 30,000 cells per microliter
• D. Approximately 50,000 to 100,000 cells per microliter

Answer: (B)

Normal adult white blood cell counts are about 4,000 to 11,000 cells per microliter. This range reflects typical immune system levels in a healthy person. Counts below this can indicate leukopenia, which may arise from bone marrow suppression or certain illnesses, while counts above suggest leukocytosis, often due to infection, inflammation, stress, or hematologic disorders. The other ranges are outside what is expected in a healthy adult—1,000 to 2,000 is too low, and 20,000 to 30,000 or 50,000 to 100,000 are far too high and usually signal acute illness or other problems.