in response to a wide variety of conditions, including viral, bacterial, fungal, or parasitic infection, cancer, hemorrhage, and exposure to certain medications or chemicals including steroids. For lung diseases such as pneumonia and tuberculosis, WBC count is very important for the diagnosis of the disease, as leukocytosis is usually present. The mechanism that causes leukocytosis can be of several forms: an increased release of leukocytes from bone marrow storage pools, decreased margination of leukocytes onto vessel walls, decreased extravasation of leukocytes from the vessels into tissues, or an increase in number of precursor cells in the marrow. Certain medications, including corticosteroids, lithium and beta agonists, may cause leukocytosis. Leukocytosis is an expected finding in healthy women during the post-partum period and is not a cause for alarm unless accompanied by clinical manifestations of infection. Diagnosis Leukocyte counts Below are blood reference ranges for various types of leukocytes/WBCs. The 97.5 percentile (right limits in intervals in image, showing 95% prediction intervals) is a common limit for defining leukocytosis. Treatment While treatment is usually not necessary in the majority of cases, hyperleukocytosis (WBC count > 50 or 100 × 109/L), which can be seen in some leukemic patients, is treated to prevent leukostasis. See also Bacterial infection Complete blood count Leukocytosis in head trauma White blood cell References External links Blood disorders Hematopathology