White Blood Cell Count (WBC; Leukocyte Count)

White Blood Cell Count (WBC; Leukocyte Count)

White blood cells (or leukocytes) are divided into two main groups: granulocytes and agranulocytes. The granulocytes receive their name from the distinctive granules that are present in the cytoplasm of neutrophils, basophils, and eosinophils. However, each of these cells also contains a multilobed nucleus, which accounts for their also being called polymorphonuclear leukocytes.

White Blood Cell Count (WBC; Leukocyte Count)

In laboratory terminology, they are often called “polys” or PMNs. The nongranulocytes, which consist of the lymphocytes and monocytes, do not contain distinctive granules and have nonlobular nuclei that are not necessarily spherical. The term mononuclear leukocytes is applied to these cells.

The endocrine system is an important regulator of the number of leukocytes in the blood. Hormones affect the production of leukocytes in the blood-forming organs, their storage and release from the tissue, and their disintegration. A local inflammatory process exerts a definite chemical effect on the mobilization of leukocytes. The life span of leukocytes varies from 13 to 20 days, after which the cells are destroyed in the lymphatic system; many are excreted from the body in fecal matter.

Leukocytes fight infection and defend the body by a process called phagocytosis, in which the leukocytes actually encapsulate foreign organisms and destroy them. Leukocytes also produce, transport, and distribute antibodies as part of the immune response to a foreign substance (antigen).


The WBC serves as a useful guide to the severity of the disease process. Specific patterns of leukocyte response can be expected in various types of diseases as determined by the differential count (percentages of the different types of leukocytes).

Leukocyte and differential counts, by themselves, are of little value as aids to diagnosis unless the results are related to the clinical condition of the patient; only then is a correct and useful interpretation possible.

Reference Values

Normal Black adults: 3.2–10.0 × 10 3/cells/mm3 or × 10 9/L or 3200–10,000 cells/mm3

Adults: 4.5–10.5 × 103/cells/mm3 or × 109/L or 4500–10,500 cells/mm3

Children: 0–2 weeks: 9.0–30.0 × 103/cells/mm3 or × 10 9/L or 9000–30,000 cells/mm3 2–8 weeks: 5.0–21.0 × 103/cells/mm3 or × 10 9/L or 5000–21,000 cells/mm3 2 months–6 years: 5.0–19.0 × 103/cells/mm3 or × 109/L or 5000–19,000 cells/mm3 6–18 years: 4.8–10.8 × 103/cells/mm3 or × 109/L or 4800–10,800 cells/mm3

Different labs have slightly different reference values


1. Obtain a venous anticoagulated EDTA blood sample of 5 mL or a finger-stick sample. Place a specimen in a biohazard bag.

2. Record the time when specimen was obtained (eg, 7:00 a.m.).

3. Blood is processed either manually or automatically, using an electronic counting instrument such as the Coulter counter or Abbott Cell-Dyne.

Clinical Implications

1. Leukocytosis: WBC greater than 11,000/mm3 or greater than 11.0 × 103/mm3 (or greater than11 × 109/L) A. It is usually caused by an increase of only one type of leukocyte, and it is given the name of the type of cell that shows the main increase:

1. Neutrophilic leukocytosis or neutrophilia

2. Lymphocytic leukocytosis or lymphocytosis

3. Monocytic leukocytosis or monocytosis

4. Basophilic leukocytosis or basophilia

5. Eosinophilic leukocytosis or eosinophilia

B. An increase in circulating leukocytes is rarely caused by a proportional increase in leukocytes of all types. When this does occur, it is usually a result of hemoconcentration.

C. In certain diseases (eg, measles, pertussis, sepsis), the increase of leukocytes is so great that the blood picture suggests leukemia. Leukocytosis of a temporary nature (leukemoid reaction) must be distinguished from leukemia. In leukemia, the leukocytosis is permanent and progressive.

D. Leukocytosis occurs in acute infections, in which the degree of increase of leukocytes depends on severity of the infection, patient’s resistance, patient’s age, and marrow efficiency and reserve.

E. Other causes of leukocytosis include the following: Leukemia, myeloproliferative disorders | Trauma or tissue injury (e.g., surgery) Malignant neoplasms, especially bronchogenic carcinoma | Toxins, uremia, coma, eclampsia, thyroid storm | Drugs, especially ether, chloroform, quinine, epinephrine (Adrenalin), colony -stimulating factors Acute hemolysis | Hemorrhage (acute) | after splenectomy | Polycythemia Vera | Tissue necrosis

F. Occasionally, leukocytosis is found when there is no evidence of clinical disease. Such findings suggest the presence of:

1. Sunlight, ultraviolet irradiation

2. Physiologic leukocytosis resulting from excitement, stress, exercise, pain, cold or heat, anesthesia

3. Nausea, vomiting, seizures

G. Steroid therapy modifies the leukocyte response.

1. When corticotrophin (adrenocorticotropic hormone, or ACTH) is given to a healthy person, leukocytosis occurs.

2. When ACTH is given to a patient with severe infection, the infection can spread rapidly without producing the expected leukocytosis; therefore, what would normally be an important sign is obscured.

2. Leukopenia: WBC less than 4000/mm3 or less than 4.0 × 103

/mm3 or less than 4.0 cells × 109/L occurs during and following:

a. Viral infections, some bacterial infections, overwhelming bacterial infections

b. Hypersplenism

c. Bone marrow depression caused by heavy-metal intoxication, ionizing radiation, drugs: Antimetabolites | Barbiturates | Benzene | Antibiotics | Antihistamines | Anticonvulsive
Ant thyroid drugs | Arsenicals | Cancer chemotherapy (causes a decrease in leukocytes; leukocyte count is used as a link to disease) | Cardiovascular drugs | Diuretics | Analgesics and anti-inflammatory drugs

d. Primary bone marrow disorders: Leukemia (aleukemic) | Pernicious anemia | Aplastic anemia | Myelodysplastic syndromes | Congenital disorders | Kostmann’s syndrome | Reticular agenesis | Cartilage-hair hypoplasia | Shwachman-Diamond syndrome | Chédiak-Higashi syndrome | Immune-associated neutropenia | Marrow-occupying diseases (fungal infection, metastatic tumor)

Interfering Factors

1. Hourly rhythm: there is an early-morning low level and late-afternoon high peak.
2. Age: in newborns and infants, the count is high (10,000/mm3 to 20,000/mm3 or 10 × 109/L to 20 × 109/L); the count gradually decreases in children until the adult values are reached between 18 and 21 years of age.
3. Any stressful situation that leads to an increase in endogenous epinephrine production and a rapid rise in the leukocyte count.



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