While the range of a normal white blood cell count is the same for everyone, the normal range of 4,000 to 11,000 is a wide one. Actual white blood cell counts vary depending on a person's gender and size, according to Cancer Research UK.
Age also affects the normal white blood cell count range. White blood cell counts rise or fall in response to various medical conditions, explains Healthline. Diseases and conditions, including HIV, bone marrow disorders, lupus and severe infections of many kinds, can cause the white blood cell count to drop. Anemia, leukemia, stress and allergies, among other conditions, can cause the white blood cell count to increase above the normal range.