Blood Cell Count & Infections

The blood cell count is a laboratory test that checks the levels of three types of cells: the red blood cells, which carry oxygen to the body’s tissues; the platelets, which help clot off blood; and the white blood cells, which fight infections. The cell count is a valuable lab work that health providers use to screen for infections, inflammation and allergic reactions.

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According to MedlinePlus, there are five types of white blood cells, also known as leukocytes, which are the cells that fight infections: basophils, eosinophils, lymphocytes, monocytes and neutrophils. Each of these cell types has a specific function. Neutrophils usually fight off bacterial infections; eosinophils can be elevated during allergic reactions or parasitic infections; lymphocytes can be elevated in viral infections; monocytes help fight viruses, parasites and infections such as tuberculosis; and basophils are involved in the body’s allergic response.


During an infection, your body produces a greater number of white blood cells. This is called leukocytosis. Depending on the type of infection, one of the specific white blood cell types may be elevated more than others. For example, during bacterial infections, neutrophils are elevated. During serious bacterial infections, the body starts producing neutrophils so fast that it starts to put into the bloodstream immature neutrophils, called bands. A high number of bands is called bandemia or a left-shift in the cell count.


The white blood cells work in concert with the immune system when the body detects an infection. The bone marrow produces them and increases or decreases their numbers as needed. According to the Puget Sound Blood Center, when an infection appears in the bloodstream, lymphocytes produce antibodies that mark the invading pathogens for destruction by neutrophils and monocytes. The macrophages, a form of monocyte, actually engulf bacteria and destroy them with various chemicals and enzymes.


Another effect of certain infections is to lower the white blood cell count. A decrease in the level of white blood cells is called leucopenia. According to MedlinePlus, infections with certain viruses, such as parvovirus, can suppress the production of these cells in the bone marrow. A decrease in the number of neutrophils, called neutropenia, can hinder the body’s defenses. This can lead to serious bacterial infections.


Although infections are one of the most common causes of an increase in white blood cells levels, other conditions can cause the same reaction. For example, leukemia, a cancer of the white blood cells, can present with abnormalities in the number and function of these cells. In fact, frequent or recurrent infections are one of the main symptoms of leukemia.