A white blood cell (WBC) count is a blood test that measures the number of white blood cells circulating in your bloodstream. These cells are a component of the immune system, produced in the bone marrow and found in blood and lymph tissue. Their primary role is to combat infections and other diseases. This measurement is a common part of a complete blood count (CBC), a routine test used to assess overall health.
The Different Types of White Blood Cells
The total WBC count combines five distinct types of white blood cells, each with a specialized function. The most numerous are neutrophils, which serve as the first line of defense against bacterial and fungal infections. Lymphocytes are the next major group; they are central to fighting viral infections and include T-cells, B-cells that produce antibodies, and natural killer cells.
Monocytes contribute by cleaning up damaged cells and breaking down bacteria. Eosinophils are tasked with destroying parasites and cancer cells, and they also play a role in allergic responses. Finally, basophils are involved in the body’s allergic response, releasing chemicals like histamine. A test called a WBC count with differential breaks down the total count into the percentage of each cell type, offering a more detailed view of immune activity.
Understanding Normal and Abnormal Ranges
A typical reference range for a total white blood cell count in adults is between 4,000 and 11,000 cells per microliter of blood. These normal ranges can vary slightly between laboratories depending on the equipment and techniques used. A result showing a higher than normal WBC count is medically termed leukocytosis. Conversely, a count that falls below the normal range is known as leukopenia.
Causes of a High White Blood Cell Count
A high WBC count (leukocytosis) most often signals the immune system is fighting an infection, particularly one caused by bacteria. It can also be a response to inflammation from injuries, burns, or chronic conditions like rheumatoid arthritis. Severe physical and emotional stress can trigger an increase in white blood cell production. Certain medications, such as corticosteroids and lithium, are known to raise WBC levels, and lifestyle factors like smoking and obesity have also been linked to elevated counts. In other cases, a persistently high count may point toward bone marrow disorders or certain cancers like leukemia.
Causes of a Low White Blood Cell Count
A low white blood cell count (leukopenia) can result from many viral infections, like influenza or hepatitis, that temporarily disrupt bone marrow function. Some severe infections, such as sepsis, can also lead to a low count because white blood cells are used up faster than they can be produced. Autoimmune disorders, including lupus, may cause the immune system to attack and destroy its own white blood cells.
Cancer treatments, such as chemotherapy and radiation therapy, are common causes as they can damage the bone marrow. A range of other medications, including some antibiotics and antipsychotics, can also suppress white blood cell production. Additionally, conditions that directly affect the bone marrow, such as aplastic anemia or certain congenital disorders, can result in chronically low WBC counts.