Leukocytosis is a condition in which the white cell (

leukocyte White blood cells, also called leukocytes or leucocytes, are the cells of the immune system that are involved in protecting the body against both infectious disease and foreign invaders. All white blood cells are produced and derived from mult ...

count) is above the normal range in the

blood Blood is a body fluid in the circulatory system of humans and other vertebrates that delivers necessary substances such as nutrients and oxygen to the cells, and transports metabolic waste products away from those same cells. Blood in the cir ...

. It is frequently a sign of an inflammatory response, most commonly the result of

infection An infection is the invasion of tissues by pathogens, their multiplication, and the reaction of host tissues to the infectious agent and the toxins they produce. An infectious disease, also known as a transmissible disease or communicable di ...

, but may also occur following certain parasitic infections or

bone tumor A bone tumor is an abnormal growth of tissue in bone, traditionally classified as noncancerous (benign) or cancerous (malignant). Cancerous bone tumors usually originate from a cancer in another part of the body such as from lung, breast, thyro ...

s as well as

leukemia Leukemia ( also spelled leukaemia and pronounced ) is a group of blood cancers that usually begin in the bone marrow and result in high numbers of abnormal blood cells. These blood cells are not fully developed and are called ''blasts'' or ...

. It may also occur after strenuous exercise, convulsions such as epilepsy, emotional stress, pregnancy and labor, anesthesia, as a side effect of medication (e.g.,

lithium Lithium (from el, λίθος, lithos, lit=stone) is a chemical element with the symbol Li and atomic number 3. It is a soft, silvery-white alkali metal. Under standard conditions, it is the least dense metal and the least dense soli ...

), and epinephrine administration. There are five principal types of leukocytosis: #

Neutrophilia Neutrophilia (also called neutrophil leukocytosis or occasionally neutrocytosis) is leukocytosis of neutrophils, that is, a high number of neutrophils in the blood. Because neutrophils are the main type of granulocytes, mentions of granulocytos ...

(the most common form) # Lymphocytosis # Monocytosis #

Eosinophilia Eosinophilia is a condition in which the eosinophil count in the peripheral blood exceeds . Hypereosinophilia is an elevation in an individual's circulating blood eosinophil count above 1.5 x 109/ L (i.e. 1,500/ μL). The hypereosinophilic sy ...

Basophilia Basophilia is the condition of having greater than 200 basophils/μL in the venous blood. Basophils are the least numerous of the myelogenous cells, and it is rare for their numbers to be abnormally high without changes to other blood components ...

This increase in leukocyte (primarily neutrophils) is usually accompanied by a "left upper shift" in the ratio of immature to mature neutrophils and macrophages. The proportion of immature leukocytes increases due to proliferation and inhibition of granulocyte and monocyte precursors in the bone marrow which is stimulated by several products of inflammation including C3a and G-CSF. Although it may indicate illness, leukocytosis is considered a laboratory finding instead of a separate

disease A disease is a particular abnormal condition that negatively affects the structure or function of all or part of an organism, and that is not immediately due to any external injury. Diseases are often known to be medical conditions that a ...

. This classification is similar to that of

fever Fever, also referred to as pyrexia, is defined as having a temperature above the normal range due to an increase in the body's temperature set point. There is not a single agreed-upon upper limit for normal temperature with sources using val ...

, which is also a test result instead of a disease. "Right shift" in the ratio of immature to mature

neutrophils Neutrophils (also known as neutrocytes or heterophils) are the most abundant type of granulocytes and make up 40% to 70% of all white blood cells in humans. They form an essential part of the innate immune system, with their functions varying ...

is considered with reduced count or lack of "young neutrophils" (metamyelocytes, and band neutrophils) in

blood smear A blood smear, peripheral blood smear or blood film is a thin layer of blood smeared on a glass microscope slide and then stained in such a way as to allow the various blood cells to be examined microscopically. Blood smears are examined in th ...

, associated with the presence of "giant neutrophils". This fact shows suppression of bone marrow activity, as a hematological sign specific for

pernicious anemia Pernicious anemia is a type of vitamin B12 deficiency anemia, a disease in which not enough red blood cells are produced due to the malabsorption of vitamin B12. Malabsorption in pernicious anemia results from the lack or loss of intrinsic ...

and radiation sickness. A leukocyte count above 25 to 30 × 10⁹/ L is termed a ''

leukemoid reaction The term leukemoid reaction describes an increased white blood cell count (> 50,000 cells/μL), which is a physiological response to stress or infection (as opposed to a primary blood malignancy, such as leukemia). It often describes the presence o ...

'', which is the reaction of a healthy bone marrow to extreme stress, trauma, or infection. It is different from

and from

leukoerythroblastosis Anemia or anaemia (British English) is a blood disorder in which the blood has a reduced ability to carry oxygen due to a lower than normal number of red blood cells, or a reduction in the amount of hemoglobin. When anemia comes on slowly, t ...

, in which either immature white blood cells (acute leukemia) or mature, yet non-functional, white blood cells (chronic leukemia) are present in peripheral blood.

Classification

Leukocytosis can be subcategorized by the type of white blood cell that is increased in number. Leukocytosis in which

are elevated is

neutrophilia Neutrophilia (also called neutrophil leukocytosis or occasionally neutrocytosis) is leukocytosis of neutrophils, that is, a high number of neutrophils in the blood. Because neutrophils are the main type of granulocytes, mentions of granulocytos ...

; leukocytosis in which

lymphocyte A lymphocyte is a type of white blood cell (leukocyte) in the immune system of most vertebrates. Lymphocytes include natural killer cells (which function in cell-mediated, cytotoxic innate immunity), T cells (for cell-mediated, cytotoxic a ...

count is elevated is lymphocytosis; leukocytosis in which

monocyte Monocytes are a type of leukocyte or white blood cell. They are the largest type of leukocyte in blood and can differentiate into macrophages and conventional dendritic cells. As a part of the vertebrate innate immune system monocytes also ...

count is elevated is monocytosis; and leukocytosis in which

eosinophil Eosinophils, sometimes called eosinophiles or, less commonly, acidophils, are a variety of white blood cells (WBCs) and one of the immune system components responsible for combating multicellular parasites and certain infections in vertebrates. A ...

count is elevated is

eosinophilia Eosinophilia is a condition in which the eosinophil count in the peripheral blood exceeds . Hypereosinophilia is an elevation in an individual's circulating blood eosinophil count above 1.5 x 109/ L (i.e. 1,500/ μL). The hypereosinophilic sy ...

.Table 12-6 in: 8th edition. An extreme form of leukocytosis, in which the WBC count exceeds 100,000/µL, is leukostasis. In this form there are so many WBCs that clumps of them block

blood flow Hemodynamics or haemodynamics are the dynamics of blood flow. The circulatory system is controlled by homeostatic mechanisms of autoregulation, just as hydraulic circuits are controlled by control systems. The hemodynamic response continuously m ...

. This leads to ischemic problems including

transient ischemic attack A transient ischemic attack (TIA), commonly known as a mini-stroke, is a minor stroke whose noticeable symptoms usually end in less than an hour. TIA causes the same symptoms associated with strokes, such as weakness or numbness on one side of ...

and

stroke A stroke is a disease, medical condition in which poor cerebral circulation, blood flow to the brain causes cell death. There are two main types of stroke: brain ischemia, ischemic, due to lack of blood flow, and intracranial hemorrhage, hemorr ...

Causes

Leukocytosis is very common in acutely ill patients. It occurs 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 Bone marrow is a semi-solid biological tissue, tissue found within the Spongy bone, spongy (also known as cancellous) portions of bones. In birds and mammals, bone marrow is the primary site of new blood cell production (or haematopoiesis). It i ...

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

corticosteroid Corticosteroids are a class of steroid hormones that are produced in the adrenal cortex of vertebrates, as well as the synthetic analogues of these hormones. Two main classes of corticosteroids, glucocorticoids and mineralocorticoids, are inv ...

and

beta agonists Beta adrenergic agonists or beta agonists are medications that relax muscles of the airways, causing widening of the airways and resulting in easier breathing. They are a class of sympathomimetic agents, each acting upon the beta adrenoceptors. ...

, 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 Reference ranges (reference intervals) for blood tests are sets of values used by a health professional to interpret a set of medical test results from blood samples. Reference ranges for blood tests are studied within the field of clinical chemis ...

for various types of leukocytes/WBCs. The 97.5 percentile (right limits in intervals in image, showing 95%

prediction interval In statistical inference, specifically predictive inference, a prediction interval is an estimate of an interval in which a future observation will fall, with a certain probability, given what has already been observed. Prediction intervals are ...

s) 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.

References

External links

{{Lymphatic disease Blood disorders Hematopathology