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White blood cells (WBCs), or leukocytes, fight infection and defend the body through a process called phagocytosis, in which the leukocytes encapsulate and destroy foreign organisms. WBCs also produce, transport, and distribute antibodies as part of the immune response to a foreign substance, or antigen.


The WBC count serves as an indicator of disease process severity; specific WBC response patterns are expected in various diseases, as determined by the differential count (percentage of different WBC types). WBC and differential counts by themselves are of little value as diagnostic aids until the results are related to the clinical status of the patient; only then is a correct and useful interpretation possible. Signs and symptoms associated with increased WBCs (leukocytosis) include fever and fatigue.


Normal reference values in adults


* Black adults: 3.2-10.0 x 103/mm3 or 3,200-10,000/mm3.(Due to a condition called benign ethnic neutropenia, many people with African ancestry have a persistently low WBC count.1)


* All other adults: 4.5-10.5 x 103/mm3 or 4,500-10,500/mm3.


Possible causes of leukocytosis

(WBC count > 11.0 x 103/mm3 or WBC count > 11,000/mm3)


* acute infections


* leukemia and myeloproliferative disorders


* trauma or tissue injury


* malignant neoplasms


* toxins, uremia, or a thyroid storm


* drugs (steroids or epinephrine)


* tissue necrosis.



Possible causes of leukopenia

(WBC count < 4.0 x 103/mm3 or WBC count < 4,000/mm3)


* viral infections and overwhelming bacterial infections


* hypersplenism


* bone marrow depression caused by heavy metal intoxication, ionizing radiation, and medications such as chemotherapy


* primary bone marrow disorders


* immune-associated neutropenia.



Critical values


* WBC count < 2.0 x 103/mm3 or WBC count < 2,000/mm3


* WBC count > 11.0 x 103/mm3 or WBC count > 11,000/mm3)




1. Reich D, Nalls MA, Kao WH, et al Reduced neutrophil count in people of African descent is due to a regulatory variant in the Duffy antigen receptor for chemokines gene. PLoS Genet. 2009;5(1):e1000360. [Context Link]


Source: Fischbach F, Dunning MB III. A Manual of Laboratory and Diagnostic Tests. 9th ed. Philadelphia, PA: Wolters Kluwer Health/Lippincott Williams and Wilkins; 2015.