What is the normal reference range for white blood cell count (WBC) in mm3?

• A. 4,000-10,000 mm3
• B. 10,000-15,000 mm3
• C. 1,000-4,000 mm3
• D. 20,000-30,000 mm3

Answer: (A)

White blood cell count is a measure of the immune cells in blood, and a healthy adult usually falls within a broad range. The standard reference range is about four thousand to ten thousand white blood cells per cubic millimeter of blood, with some labs accepting a slightly higher upper limit. This range is used because most healthy people have values in it; numbers below suggest leukopenia, while numbers above suggest leukocytosis, which can occur with infections, inflammation, or other conditions. Among common answer choices, the one that reflects this moderate-to-wide healthy range is the best fit. The other options represent counts that are clearly too low or too high for a normal, healthy individual.