White blood cells are much less numerous than red blood cells; the ratio between the two is around 1:700. [1] It is clear that white blood cells are much different than 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?
There are several different kinds of white blood 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.
The white cells go wrong in leukemia. [3] 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. [1]
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. [4] 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 the 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. [5] A single macrophage is commonly 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. Monocytes and their macrophage and dendritic-cell progeny serve three main functions in the immune system:
- Phagocytosis
- Antigen presentation
- Cytokine production
Neutrophils are the most abundant (40% to 75%) of the white blood cells. They squeeze through the capillary walls and into infected tissue where they kill invaders such as bacteria and then engulf the remnants by phagocytosis. This is a never-ending task; even in healthy people's throats, nasal passages and the 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. [6] If that happens, formerly harmless bacteria begin to proliferate, and the resulting opportunistic infections can be life threatening.
Eosinophils' number in the blood is normally quite low, 0–450/µl. However, their numbers increase sharply in the case of certain diseases, especially infections by parasitic worms. [7] Eosinophils are cytotoxic, releasing the contents of their granules on the invader killing it.
Basophils' number also increases during infection. [8] 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
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. [9]
Definition Of White Blood Cell Count
A white blood cell count or leukocyte count is, simply said, 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. [10]
A low white blood cell count is termed leucopenia, and a high white blood cell count is termed leukocytosis.
What Does The WBC Test Result Mean?
Since reference values are dependent on many factors including [12]:
- Patient age
- Gender
- Sample population
- 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.
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 (leukopenia) may indicate [12]:
- Bone marrow failure, possibly due to infection or cancer
- Cancer and/or tumor
- Fibrosis
- The presence of a cytotoxic substance
- Collagen-vascular diseases (such as lupus erythematosus, a disease of the liver or spleen),
- Radiation
- Crohn's disease
- Infections, such as tuberculosis (TB) or certain viruses like HIV
- Lupus (also called systemic lupus erythematosus
- Rheumatoid arthritis
- Some medicines, such as those that treat infections, high blood pressure, or seizures
A high WBC count (leukocytosis) may indicate infectious diseases, an 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 [13]:
- Excessive bleeding
- Fainting or feeling light-headed
- Hematoma or blood accumulating under the skin
- Bruising
- Infection (a slight risk any time the skin is broken)
- Multiple punctures to locate veins
Drugs that may increase WBC counts include [10]:
- Epinephrine
- Allopurinol
- Aspirin
- Chloroform
- Heparin
- Quinine
- Corticosteroids
- Triamterene
Medicines that may decrease WBC counts include [10]:
- Antibiotics
- Anticonvulsants
- Antihistamines
- Antithyroid drugs
- Arsenicals
- Barbiturates
- Chemotherapeutic agents
- Diuretics
- 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 or she will know if you need treatment. A low white blood cell count usually requires further investigation and therapy.