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Blood is a liquid connective tissue made from different types of blood cells and a liquid, called plasma. The major function of blood is to carry oxygen and essential nutrients to all parts of the body. There are three types of blood cells: red blood cells (erythrocytes), white blood cells and platelets. White blood cells, also called leukocytes, are the main cells of the immune system. They fight invading harmful organisms like bacteria and viruses and protect the body against infections. White blood cells are produced in the bone marrow. They are colorless and asymmetrical in shape. They have a short lifespan, from few days to few weeks. White blood cell count is considered as an important criteria to diagnose various health conditions.

Types of White Blood Cells

There are two main categories of white blood cells such as granulocytes and agranulocytes, based on the presence of granules in the cytoplasm of the cells. There are three types of granulocytes, namely, neutrophils, eosinophils and basophils. Agranulocytes are categorized as monocytes and lymphocytes. Neutrophils, also called polymorphonuclear leukocytes, play a major role in the body’s defense system. They kill bacteria through the process of phagocytosis. These cells are present in the pus near the sites of injury or infection. Eosinophils mainly attack parasites. They are responsible for allergic reactions. Basophils secrete heparin and histamine and contribute to hypersensitivity reactions within the body.

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, damaged cells from the body. Lymphocytes are directly associated with the immune system. These cells produce antibodies against the toxins secreted by microorganisms.

White Blood Cell Count

White blood cell count is a very important diagnostic factor to detect a number of health problems such as infections, bone marrow disorders and inflammatory diseases. It is also used to monitor the response of the body to various treatments. White blood cell count is a good criteria to evaluate bone marrow function. White blood cell count constitutes the total number of leukocytes and the differential leukocyte count. In differential count, the percentage of each type of leukocyte is measured.

The normal count of leukocytes is 4,000-11,000/mm3. The average count is 7,000/mm3. If the leukocyte count is below 4,000, then the condition is known as leukopenia. There may be decrease in the percentage of each type of leukocytes. For example, decrease in the number of neutrophils is known as neutropenia. If the count is higher than 11,000, then it is referred to as leukocytosis. There may be increase in each type of white blood cells like neutrophilia, eosinophilia, basophilia, monocytosis and lymphocytosis.

The percentage of each type of white blood cells can be obtained through the differential leukocyte count. The normal percentage of granulocytes and agranulocytes is as follows:

• 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)

Luekopenia or leukocytosis can occur due to different reasons and health conditions. Let’s understand in detail about it.

What causes Low White Blood Cell Count?

Low white blood cell count or leukopenia is caused by various medical conditions such as chemotherapy, radiotherapy, aplastic anemia, autoimmune diseases like lupus, spleen disease, liver diseases and viral infections. A deficiency of vitamins and certain minerals like copper and zinc can also lead to leukopenia. Leukopenia can result from certain bone marrow diseases such as myelodysplastic syndrome. Medications like immunosuppressive drugs, certain antibiotics, antithyroid drugs, diuretics and chemotherapy drugs can also lead to leukopenia. Low blood cell count leads to a weakened immune system, making the body more susceptible to bacterial, viral or fungal infections.

What causes High White Blood Cell Count?

High white blood cell count or leukocytosis is caused by anemia, infections, allergies, systemic diseases, inflammatory diseases like rheumatoid arthritis, tissue damage caused by burns, leukemia and physical or emotional stress. Certain medications like heparin, corticosteroids, quinine and anti-seizure drugs can also increase white blood cell count. A newborn has high white blood cell count 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.

How is White Blood Cell Count Done?

When the doctor suspects infection or any disorder that can affect the leukocyte count, then a white blood cell count test is recommended. White blood cell count 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. Blood sample is obtained from a venous or fingerprick blood collection. In infants, heel stick is the most preferred method for blood collection. White blood cell count can be done through a manual method or by using automated cell counters. Absolute count of each type of leukocytes e.g. the absolute neutrophil count, absolute lymphocyte count or absolute eosinophil count, 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.