White blood cells (leukocytes) fight infections. More white blood cells are produced when a foreign organism is detected. A high white blood count (leukocytosis) could indicate an underlying medical condition and requires further medical evaluation.
White blood cells are produced by bone marrow.
High white blood cell counts may indicate inflammation, trauma, allergies, leukemia or infections, or they may simply be the result of intense exercise.
There are five different types of white blood cells, and they each serve a different function in the body. The types are neutrophils, lymphocytes, monocytes, eosinophils and basophils. The type of white blood cell with an elevated count can indicate a specific disease. For example, a high monocyte count may indicate a bacterial infection, while a high neutrophil count may indicate cancer.
The normal white blood cell count is between 4,500 and 10,000 cells per microliter.
A high white blood count always merits further evaluation, but in some cases it is normal. Women in their ninth month of pregnancy, heavy smokers, newborns and those who have had their spleen removed can have normally elevated white blood cell counts.