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White blood cells are much less numerous than red; the ratio between the two is around 1:700. White blood cells have nuclei, participate in protecting the body from infection, and consist of lymphocytes and monocytes with relatively clear cytoplasm, and three types of granulocytes, whose cytoplasm has granules. It is clear that white blood cells are much different then other cells of our body. These cells have an important role, so a doctor will often wish to see a patient’s white blood cell count. But what exactly is a low white blood cell count, since this is a common test result?

What are white blood cells?

The white blood cells are important defenders against infection. A blood count is used to count the number of white cells and tells the doctor which types of white cells are present. There are several different kinds of white cells, each of them specializing in defending the human organism from a particular infection. It’s like having an army - navy, marines and air force - in reserve for each type of invasion. Depending on the type of infection, the navy or air force will activate.
We have a resting level of white cells in our blood; here they simply circulate and ensure our body is safe against infection. If you develop an infection, the number of white cells that specialize in that kind of infection will suddenly increase. If you do a blood test, it will show a raised white cell count. A different white cell comes up when someone has, for instance, glandular fever then appendicitis. Therefore, a doctor can tell from a blood count if you have had an infection, and he has a clue what kind of infection by the type of white cell that has increased in number.

The white cells go wrong in leukemia. Therefore, a simple blood count will eliminate the worry about leukemia if your doctor suspects it. Different types of white blood cells have different roles.

* Lymphocytes are one group; there are several kinds of lymphocytes, although they all look alike under the microscope.

Each of these lymphocytes has a different function to perform. The most common types of lymphocytes are B-lymphocytes, responsible for making antibodies. T-lymphocytes or T-cells are also important, with several subsets of these cells. Inflammatory T-cells recruit macrophages and neutrophils to the site of infection or other tissue damage. Cytotoxic T-lymphocytes kill virus-infected and potential tumor cells, while helper T-cells enhance the production of antibodies by B-cells. Although bone marrow is the ultimate source of lymphocytes, the lymphocytes that will become T-cells migrate from the bone marrow to the thymus, where they mature. Both B-cells and T-cells also take up residence in lymph nodes, the spleen and other tissues where they encounter antigens, continue to divide by mitosis, and mature into fully functional cells.

* Monocytes leave the blood and become macrophages. It is a common situation that a single macrophage is surrounded by several lymphocytes. Macrophages are large, phagocytic cells that engulf foreign material called antigens that enter the body, and also dead and dying cells of the body.

* Neutrophils are the most abundant of the white blood cells. They squeeze through the capillary walls and into infected tissue where they kill the invaders such as bacteria and then engulf the remnants by phagocytosis. This is a never-ending task; even in healthy people throat, nasal passages, and colon harbor vast numbers of bacteria. Most of these are commensals, and do us no harm - but that is because neutrophils keep them in check. However, heavy doses of radiation, chemotherapy, and many other forms of stress can reduce the numbers of neutrophils. If that happens, formerly harmless bacteria begin to proliferate, and the resulting opportunistic infection can be life threatening.

* Eosinophils number in the blood is normally quite low, 0–450/µl. However, their numbers increase sharply in case of certain diseases, especially infections by parasitic worms. Eosinophils are cytotoxic, releasing the contents of their granules on the invader killing it.

* Basophils number also increases during infection. Basophils leave the blood and accumulate at the site of the infection or other inflammation, discharging the contents of their granules, releasing a variety of mediators such as histamine, serotonin, prostaglandins and leukotrienes. These substances increase the blood flow to the area and in other ways add to the inflammatory process. The mediators released by basophils also play an important part in some allergic responses such as hay fever and an anaphylactic response to insect stings.

How to use white blood cell tests

Conditions or medications that weaken the immune system, such as HIV infection or chemotherapy, cause a decrease in white blood cells, so the white blood cell (WBC) count detects dangerously low numbers of these cells. The WBC count helps to suggest the presence of an infection or leukemia. It is also used to help monitor the body’s response to various treatments and to monitor bone marrow function as well.

Definition of white blood cell count

White blood cell count or leukocyte count is the number of white blood cells in the blood. The doctor will usually measure WBC as part of the CBC, or complete blood count. White blood cells are the infection-fighting cells in the blood, and are distinct from the red oxygen-carrying blood cells, known as erythrocytes. All the types of white blood cells are reflected in the white blood cell count. The normal range for the white blood cell count varies between laboratories, but is usually between 4,300 and 10,800 cells per cubic millimeter of blood. This can also be refered to as the leukocyte count, and expressed in international units as 4.3-10.8 x 109 cells per liter. A low white blood cell count is termed leucopenia, and a high white blood cell count is termed leukocytosis.

What does the test result mean?

Since reference values are dependent on many factors, including patient age, gender, sample population, and test method, numeric test results have different meanings in different labs. Your lab report should include the specific reference range for your test and you should discuss your test results with your doctor. An elevated number of white blood cells (leukocytosis) can result from bacterial infections, inflammation, leukemia, trauma, or stress. A decreased WBC count (leucopenia) can result from many different situations, such as chemotherapy, radiation therapy, or diseases of the immune system.

What can affect the results of a white blood cells test?

Eating, physical activity, and stress can cause an increased WBC count, and pregnancy in the final month and labor may be associated with increased WBC levels as well. If you have had your spleen removed, you may have a persistent mildly- to moderately-increased white blood cell count. The WBC count tends to be lower in the morning and higher in the late afternoon, and these counts are age-related as well. On average, normal newborns and infants have higher WBC counts than adults. It is common for the elderly to fail to develop leukocytosis as a response to infection. There are many drugs that cause both increased and decreased WBC counts so this fact is important to consider as well before reading the results of a white blood cell count.

A low WBC count (leucopenia) may indicate bone marrow failure, possibly due to infection, tumor, fibrosis, presence of cytotoxic substance, collagen-vascular diseases (such as lupus erythematosus, disease of the liver or spleen), or radiation.
A high WBC count (leukocytosis) may indicate infectious diseases, inflammatory disease (such as rheumatoid arthritis or allergy), leukemia, severe emotional or physical stress, tissue damage, and anemia.

The risks of a white blood cells count

Risks associated with having blood drawn are slight - excessive bleeding, fainting or feeling light-headed, hematoma or blood accumulating under the skin, infection ( a slight risk any time the skin is broken), and multiple punctures to locate veins.

Drugs that may increase WBC counts include epinephrine, allopurinol, aspirin, chloroform, heparin, quinine, corticosteroids, and triamterene as well. Medicines that may decrease WBC counts include antibiotics, anticonvulsants, antihistamine, antithyroid drugs, arsenicals, barbiturates, chemotherapeutic agents, diuretics, and sulfonamides.

Veins and arteries vary in size from one patient to another and from one side of the body to the other, so obtaining a blood sample from some people may be more difficult than from others. That is why each person that undergoes a WBC count test should talk to the doctor beforehand.

Once your doctor reads your results, he will know if you need treatment. Low white blood cells count usually require further investigation and therapy.