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Functional Blood Chemistry Manual


Marker Name: WBC


Laboratory reference range: 3.4–10.8 x 103/µL

Functional reference range: 5.0–8.0 x 103/µL


White blood cells (WBCs), also known as leukocytes, are the major cell type of the immune system. Unlike red blood cells and platelets, white blood cells have a nucleus. Five main types of leukocytes circulate in the bloodstream: basophils, neutrophils, eosinophils, monocytes, and lymphocytes. Lymphocytes can be further characterized as B lymphocytes, T lymphocytes, and natural killer (NK) cells. Monocytes and neutrophils have the ability to phagocytose, or consume microbes. Basophils and eosinophils participate in allergic responses, although eosinophils primarily respond to parasitic infections.

White blood cells are primarily produced in the bone marrow. Lymphocytes may also be produced in the lymphoid tissue, such as the spleen and lymph nodes. The bone marrow contains a mitotic pool, a maturation pool, and a storage pool of neutrophils. Leukocytes in the vasculature are either circulating or in the marginal pool; leukocytes attached to blood vessel walls at the tissue-capillary interface make up the marginal pool. Leukocytes may also cross from the circulation into the tissue pool in various tissues throughout the body. An increase in white blood cell count usually means an increase in neutrophils;1 however, an increase in WBC count may also be due to an increase in eosinophils, monocytes, lymphocytes, or (uncommonly) basophils.2

WBC levels may increase due to infection, inflammatory disorders, hematologic cancer (e.g., leukemia), corticosteroids, and stress.3 During acute inflammation, the mitotic pool grows, while the maturation and storage pools within bone marrow shrink. This decrease reflects increased release of neutrophils into the circulation.4 The number of neutrophils in the tissue pool also increases. Stress or corticosteroid administration causes neutrophils to move from the marginal pool to the circulating pool, while bone marrow pools remain unaffected. In chronic disorders such as myeloproliferative disorders or chronic myelogenous leukemia, neutrophilia is caused by increased production and release of cells.5

An elevated white blood cell count, or leukocytosis, is usually the result of a reactive leukocytosis, which means leukocyte numbers increase in response to an infection, stress, or inflammation. Conversely, leukocytosis may be clonal, which means leukocytes are being created along one cell line, as would occur during leukemia. In both reactive and clonal leukocytosis, one type of white blood cell usually predominates.3 For example, a parasitic infection may cause eosinophils to increase.6 Likewise, acute lymphocytic leukemia may cause a large increase in the absolute lymphocyte count.7

An abnormally low WBC count is called leukopenia. As with leukocytosis, leukopenia often refers to a change in the number of neutrophils, the major leukocyte. In fact, leukopenia is often used interchangeably with neutropenia.8 However, leukopenia may be due to specific reductions in leukocytes other than or in addition to neutrophils. Leukopenia may occur when white blood cells are depleted by infection or cancer treatment (e.g., chemotherapy, radiation therapy). It may also occur due to ineffective production or maturation of leukocytes in the bone marrow, which may occur in myelodysplastic syndrome or leukemia.8 White blood cells may be sequestered within the spleen, a condition called hypersplenism.

A white blood cell count or WBC is often measured in the context of a complete blood count (CBC) with differential. This includes individual counts of the five main leukocytes: neutrophils, eosinophils, basophils, lymphocytes, and monocytes. Unless a different test has been specifically ordered, a standard CBC with differential is performed using an automated cell counting device. Physicians may also order a manual differential in which laboratory personnel create a slide of the patient’s blood and manually count populations of blood cells under a microscope.9,10 This may also be called a peripheral blood smear.10

A white blood cell count may be requested in fluids other than blood. It is considered routine for cerebral spinal fluid collected during a lumbar puncture to be sent for a white blood cell count with differential.11,12 Likewise, the WBC is measured in fluid removed from the pleural space after thoracentesis, the joint space after arthrocentesis, and the abdominal cavity after paracentesis, among others.


High in:13-15

  • Normal pregnancy
  • Transient elevation during labor and delivery
  • Normal infancy
  • Cigarette smoking
  • Acute infection (especially bacterial, but also certain viral and fungal infections)
  • Inflammation
  • Chronic inflammatory conditions (e.g., rheumatoid arthritis, Crohn’s disease, ulcerative colitis, vasculitis)
  • Acute stress
  • Myeloproliferative disorders
  • Hematologic and neoplastic diseases
    • Acute lymphocytic leukemia
    • Chronic lymphocytic leukemia
    • Chronic myelogenous leukemia
    • Large granular lymphocytic leukemia
    • Thymoma
  • Metabolic disorders
    • Diabetic ketoacidosis
    • Preeclampsia
    • Uremia
  • Certain genetic abnormalities
  • Drugs
    • Glucocorticoids
    • Recombinant granulocyte colony-stimulating factor
    • Catecholamines
    • Lithium

Low in:16-18

  • Nutritional deficiency (e.g., vitamin B12, folate, copper)
  • Congenital neutropenia (e.g., benign ethnic neutropenia)
  • Infection (e.g., HIV, sepsis)
  • Post-infectious neutropenia
  • Autoimmune neutropenia
  • Myelodysplastic syndromes
  • Hematologic and neoplastic diseases
  • Aplastic anemia
  • Paroxysmal nocturnal hemoglobinuria
  • Drugs
    • Chemotherapy
    • Atypical antipsychotics (e.g., clozapine, olanzapine)
    • Antibiotics (e.g., penicillin)
    • Anticonvulsants (e.g., phenytoin)
    • Sulfasalazine
    • Thionamides (e.g., methimazole, propylthiouracil, carbimazole)
    • Ticlopidine
    • Rituximab


High in:

  • Same as conventional indications

Low in:

  • Same as conventional indications


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