White blood cells, also called leukocytes, are cells that exist in the blood, the lymphatic system, and tissues and are an important part of the body's defence system. They help protect against infections and also have a role in inflammation and allergic reactions. The white blood cell (WBC) count totals the number of white blood cells in a sample of your blood.

    The white blood cell count (WBC) is used as part of a full complete blood count (CBC) to:

    ·         Screen for a wide range of diseases and conditions

    ·         Help diagnose an infection or inflammatory process or other diseases that affect the number of WBCs, such as allergies, leukaemia or immune disorders, to name a few.

    ·         Monitor the progression of conditions such as those named above

    ·         Monitor the body's response to various treatments and/or to monitor bone marrow function; some treatments, such as radiation and chemotherapy, are known to affect white cells and may be monitored using WBC counts.

    A WBC count can be used to detect is a disease or condition affecting white blood cells, but it cannot determine the underlying cause. Several other tests may be done help make a diagnosis, such as a WBC differential, a blood smear review, or in severe conditions, a bone marrow examination. A differential may indicate which type of WBC is low or high while a blood smear and/or bone marrow biopsy can reveal the presence of abnormal and/or immature WBCs.

    A WBC count is normally ordered as part of the complete blood count (CBC), which may be performed when you have a routine health examination. The test may be done when you have general signs and symptoms of an infection and/or inflammation, such as:

    ·         Fever, chills

    ·         Body aches, pain

    ·         Headache

    ·         A variety of other signs and symptoms, depending on the site of suspected infection or inflammation

    Testing may be performed when there are signs and symptoms that a healthcare practitioner thinks may be related to a blood disorder, autoimmune disorder, or an immune deficiency.

    A WBC may be ordered on a regular basis when you have been diagnosed with an infection, blood or immune disorder or another condition affecting the number and types of WBCs. It may also be ordered periodically when you are receiving treatment for one of these conditions or when you are receiving radiation or chemotherapy.

    A WBC count indicates an overall increase or decrease in the number of white blood cells. A healthcare practitioner will consider the results of a WBC count together with results from other components of the complete blood count (CBC) as well as a number of other factors, such as physical examination, medical history, and signs and symptoms.

    A high white blood cell count, called leukocytosis, may result from a number of conditions and diseases. Some examples include:

    ·         Infections, most commonly caused by bacteria and some viruses, less commonly by fungi or parasites

    ·         Inflammation or inflammatory conditions such as rheumatoid arthritis, vasculitis or inflammatory bowel disease

    ·         Leukaemia, myeloproliferative neoplasms

    ·         Conditions that result in tissue death (necrosis) such as trauma, burns, surgery or heart attack

    ·         Allergic responses (e.g., allergies, asthma)

    A low white blood cell count, called leukopenia, can result from conditions such as:

    ·         Bone marrow damage (e.g., toxin, chemotherapy, radiation therapy, drugs)

    ·         Bone marrow disorders—the bone marrow does not produce sufficient WBCs (e.g., myelodysplastic syndrome, vitamin B12 or folate deficiency)

    ·         Lymphoma or other cancer that has spread (metastasized) to the bone marrow

    ·         Autoimmune disorders—the body attacks and destroys its own WBCs (e.g., lupus)

    ·         Dietary deficiencies (e.g., vitamin B12 deficiency)

    ·         Overwhelming infections (e.g., sepsis)

    ·         Diseases of the immune system, such as HIV, which destroy T lymphocytes

    When WBC counts are used for monitoring medical conditions, a series of WBC counts that continues to rise or fall to abnormal levels indicates that the condition or disease is getting worse. WBC counts that return to normal indicates improvement and/or successful treatment.

    The most common cause of an increase in the white blood cell count is

    ·         The normal response of the body to an infection

    Other causes include

    ·         Certain drugs, such as corticosteroids

    ·         Cancers of the bone marrow (such as leukaemia)

    ·         Release of immature or abnormal white blood cells from the bone marrow into the blood

    There are many types of white blood cell (see Overview of White Blood Cell Disorders), and each type may be increased. However, most commonly, people have an

    ·         Increase in neutrophils

    ·         Increase in lymphocytes

    Possible Causes of High and Low WBC Differential Results