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Quick Fact
Contrary to what a lot of people believe, TLC and DLC tests do not show whether a patient is suffering from a particular illness. They only show how likely he/she is to contact an infection.
White blood cells, also called leukocytes, are the soldier cells of the immune system. They fight pathogenic organisms, like bacteria and viruses, that invade the body and protect it against infections. They are produced in the bone marrow, are colorless and asymmetrical. They have a short lifespan, which may last from a few days to a few weeks. White blood cell count is considered an important criteria to diagnose various health conditions. And to take preventive measures if the likelihood of a weakened immune system exists.

Normal WBC Count
As mentioned earlier, the normal WBC count is 4,000-11,000/mm3 and the average count is 7,000/mm3. If the leukocyte count is below 4,000, then the condition is known as leukopenia. On the other hand, an abnormal increase in the number of WBCs is called leukocytosis. Leukemia is the condition where there is an abnormal spurt in the number of immature white blood cells in the blood.

Leukocytes are mainly divided into granulocytes and agranulocytes, based on the presence of granules (lipid-enveloped enzymes in the WBC that are involved in the function of engulfing pathogenic molecules) in the cytoplasm of the cells. There are three types of granulocytes (Neutrophils, Basophils, and Eusinophils) and two types of agranulocytes (Monocytes and lymphocytes)

The percentage of each type of WBC can be obtained through the differential leukocyte count (DLC). Listed below are the normal percentage ranges of granulocytes and agranulocytes:
  • Neutrophils: 50-70% (2,500-7,000 absolute count)
  • Basophils: 0.4-1% (40-100 absolute count)
  • Eosinophils: 1-3% (100-300 absolute count)
  • Monocytes: 4-6% (200-600 absolute count)
  • Lymphocytes: 25-35% (1,700-3,500 absolute count)

Different Types of WBC in Detail

As mentioned above, white blood cells can be classified under 2 broad categories, further divided into 5 subcategories, based upon their role in the comprehensive immune function. The following lines would acquaint you with each type of WBC:-

Granulocytes - WBC that contain granules in their cytoplasm
  1. Neutrophils, also called polymorphonuclear leukocytes, play a major role in the body's defense system. They disable bacteria, fungi, and foreign particles through the process of phagocytosis (ingestion), degranulation (release of enzymes to mitigate the infection), and by producing Neutrophil Extracellular Traps that ensnare pathogens and foreign particles even before they come into contact with the cells. These cells are present in the pus near the sites of injury or infection.
  2. Eosinophils mainly attack parasites of moderate to large dimensions. They are responsible for controlling allergic reactions.
  3. Basophils secrete heparin and histamine and is responsible for triggering the body's inflammatory response.
Agranulocytes - WBC that do not contain granules in their cytoplasm
  1. Monocytes are the largest type of white blood cells. They function as tissue macrophages and phagocytize bacteria as well as prevent invasion of foreign bodies. These cells also remove dead and damaged cells from the body and help in the replacement of macrophages and dendritic cells.
  2. Lymphocytes are directly associated with the immune system. These cells produce antibodies against the toxins secreted by microorganisms. Lymphocytes such as T cells are directly involved in targeting and fighting cells infected by viruses and tumor cells. T cells also regulate the body's immune function in such a way that the immune response is restored to normal levels after the infection has been taken care of. This prevents the body from turning against itself, a condition that is known as Autoimmunity. The B cells activate the T cells on suspecting a viral or malignant condition, by producing antigens.
There also exist Macrophages and Dendritic Cells that are derivatives of Monocytes and the Lymphatic System (sometimes, bone marrow), respectively. Macrophages swallow and break down cellular waste and pathogenic substances, while Dendritic Cells stimulate the T cells.

Causes of Low WBC Count

Low white blood cell count or leukopenia could be caused by various medical conditions such as:
  • Autoimmune diseases
  • Aplastic anemia
  • Spleen or liver diseases
  • Viral infections
  • A deficiency of vitamins and certain minerals like copper and zinc
  • Bone marrow disease such as myelodysplastic syndrome
Leukopenia could also be observed in people who have been taking certain drugs or those undergoing chemotherapy or radiation therapy. Prolonged use of drugs that may cause this condition include:
  • Immunosuppressive drugs such as oral contraceptives
  • Certain antibiotics
  • Antithyroid drugs
  • Diuretics
Causes of High WBC Count

High white blood cell count or leukocytosis could be caused by medical conditions such as:
  • Anemia
  • Infections
  • Allergies
  • Systemic diseases
  • Rheumatoid arthritis
  • Tissue damage caused by burns
  • Leukemia
  • Physical or emotional stress
Prolonged use of drugs that may cause this condition include:
  • Heparin
  • Corticosteroids
  • Quinine
  • Anti-seizure drugs
Note: A newborn has high count of WBCs that ranges from 9,000 to 30,000/mm3 on the day of birth. Within two weeks, the count falls to normal adult range. Leukocytosis is also common during pregnancy.

Determining WBC Count

When the doctor suspects infection or any disorder that can affect the leukocyte count, then a white blood cell count test is recommended. It is generally ordered as a part of complete blood count (CBC). CBC, also called hemogram, involves determination of hemoglobin percentage, erythrocyte count, hematocrit, total leukocyte count, differential leukocyte count, platelet count and examination of blood smear to study cytology and presence of parasites. A sample is obtained by drawing a small amount of blood from a vein or by lightly pricing the tip of a finger . In infants, heel stick is the most preferred method for blood collection. White blood cell count can be taken manually or by using automated cell counters. Absolute count of each type of leukocytes is also determined.

Thus, white blood cell count guides the doctor in the diagnosis and prognosis of any health issues of patients. Timely monitoring of leukocyte count can help you get adequate treatment at the right time and prevent potential complications. A diet rich in vitamins, minerals (especially, zinc), and antioxidants keep white blood cell count at a healthy level. Regular exercise and adequate rest also ensure that your immune system stays robust, by helping your body keep optimal reserves of WBC at all times.