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Leukocytosis is a condition characterized by an elevated number of white cells in the blood.


Leukocytosis is a condition that affects all types of white blood cells. Other illnesses, such as neutrophilia, lymphocytosis, and granulocytosis, target specific types of white blood cells. Normal white blood cell counts are 4,300-10,800 white blood cells per microliter. Leukocyte or white blood cell levels are considered elevated when they are between 15,000-20,000 per microliter. The increased number of leukocytes can occur abnormally as a result of an infection, cancer, or drug intake; however, leukocytosis can occur normally after eating a large meal or experiencing stress.

Causes and symptoms

Leukemias can cause white blood cell counts to increase to as much as 100,000. Each kind of white cell can produce a leukemia. Apart from leukemias, nearly all leukocytosis is due to one type of white blood cell, the polymorphonuclear leukocyte (PMN). These conditions are more accurately referred to as neutrophilia.

The most common and important cause of neutrophilia is infection, and most infections cause neutrophilia. The degree of elevation often indicates the severity of the infection. Tissue damage from other causes raises the white count for similar reasons. Burns, infarction (cutting off the blood supply to a region of the body so that it dies), crush injuries, inflammatory diseases, poisonings, and severe diseases, like kidney failure and diabetic ketoacidosis, all cause neutrophilia.

Counts almost as high occur in leukemoid (leukemia-like) reactions caused by infection and non-infectious inflammation.

Drugs can also cause leukocytosis. Cortisone-like drugs (prednisone), lithium, and NSAIDs are the most common offenders.

Non-specific stresses also cause white blood cells to increase in the blood. Extensive testing of medical students reveals that neutrophilia accompanies every examination. Vigorous exercise and intense excitement also cause elevated white blood cell counts.


A complete blood count (CBC) is one of the first tests obtained in any medical setting. More than 11,000 white cells in a cubic millimeter of blood is considered high. Bone marrow biopsy may help clarify the cause.


Relieving the underlying cause returns the count to normal.


Biopsy Surgical removal of tissue for examination.

Inflammation Heat, swelling, redness, and pain caused by tissue injury.

Ketoacidosis A severe stage of diabetes where acids and ketones accumulate in the body.

NSAID Non-steroidal anti-inflammatory drug such as ibuprofen.


By treating the underlying condition, white blood cell counts usually return to normal



Holland, Steven M., and John I. Gallin. "Disorders of Granulocytes and Monocytes." In Harrison's Principles of Internal Medicine, edited by Anthony S. Fauci, et al. New York: McGraw-Hill, 1997.