Read on to learn more about the WBC count, what the range of values means, and why your healthcare provider might order the test.
Purpose of the Test
White blood cells are a group of blood cells that fight infection and inflammation in the body. They also protect your body from damage due to toxins (like air pollution) and aid wound healing and tissue repair.
White blood cells are produced in the bone marrow and are an essential part of your immune system. Although they make up less than 1% of your total blood cells, they play a vital role in keeping you healthy.
A WBC count is a test that involves a simple blood draw. A healthcare practitioner will use a thin needle to collect blood from one of your veins, usually in your arm. You can generally get the test results back from the lab in a few days.
Your healthcare provider might order a WBC count if you have any of the following symptoms:
Fever Body aches Chills Night sweats Persistent or severe fatigue Swollen lymph nodes Allergy symptoms
A WBC count measures the total number of all white blood cells in your blood. There are five different types:
Neutrophils: These cells help fight bacteria and fungal infections. They usually make up 50% to 75% of all your white blood cells. Lymphocytes: These cells help fight infections and produce immune proteins called antibodies. and attack tumors. Lymphocytes are found in both your blood and lymph tissues. Monocytes: These cells help damaged or dead cells from the body. They also travel into tissues like the lungs and liver and become another type of cell that help eases inflammation. Eosinophils: These cells fight infections caused by parasites. They also respond to allergic reactions and inflammation. Basophils: These cells release a chemical called histamine during an allergic response. This triggers symptoms like a runny nose or watery eyes.
If you see these five cell types on your results along with numeric values, it is because your healthcare provider ordered a WBC differential test. The “diff” test looks at each of the cell types to figure out what’s going on in the body based on which values are either high or low. Doing so helps narrow the possible causes.
WBC counts are often part of a more comprehensive test called a complete blood cell (CBC) count. The CBC count looks not only at white blood cells but also at red blood cells (that transport oxygen throughout the body) and platelets (that are responsible for blood clotting).
A CBC count is a common test used to evaluate your overall health and detect a wide range of illnesses, including anemia, infections, and disease like leukemia.
Normal Reference Range of Values
No hard-and-fast number defines what a “normal” WBC count is. Instead, the results are reported in relation to the normal expected range of values within a population. Anything below this range is low, and anything above this range is considered high.
Labs can also differ in defining a high or a low WBC count. So, it is possible to have a normal WBC at one lab and find that you have a low or high WBC count at another. (This is why people who require ongoing blood tests are advised to use the same lab provider for all tests.)
WBC counts are measured by the number of white blood cells per cubic millimeter of blood (cells/mm3). Here is an example of how a lab might define the expected range of values for a WBC count:
If your WBC count is high, you have what is called leukocytosis. Among some of the possible causes of leukocytosis are:
A bacterial, fungal, or parasitic infectionInflammatory conditionsBurnsSteroid useCigarette smokingPregnancyLeukemia
If your WBC count is low, you are said to have leukopenia. Among some of the possible causes of leukopenia are:
A blood or bone marrow disorderAutoimmune disordersMedication side effectsChemotherapy or radiation therapyA viral infection
Abnormal WBC Count Due to Medications
Many prescription and over-the-counter drugs can cause an abnormal WBC count. It is essential always to review your medication history with your healthcare provider.
Certain drugs can cause your WBC count to drop below the normal range of values. These include:
Antibiotics: Used to treat bacterial infections Anticonvulsive drugs: Use to treat epilepsy and chronic pain Chemotherapy: Used to treat cancer Rituxan (rituximab): Used to treat autoimmune diseases and certain cancers
Some medicines can raise your WBC count. Some of the more common include:
Albuterol: Used to treat asthma and other breathing problems Beta-blockers: Used to treat high blood pressure Corticosteroid drugs: Used to reduce inflammation Epinephrine: Used to treat severe allergic reactions Heparin: A blood thinner used to prevent blood clots Lithium: Used to treat bipolar disorder
Follow-Up Tests
If your WBC count is abnormal, your healthcare provider may order additional tests depending on your symptoms and medical history. These may include tests to see if you have:
An infection: Your healthcare provider may order a urinalysis, for example, if they think you have a urinary tract infection. If they believe you have a viral infection, they might contain a polymerase chain reaction (PCR) test to identify the suspected virus. An inflammation problem: Your healthcare provider may order a C-reactive protein (CRP) test. CRP is a type of protein that increases if you have inflammation anywhere in the body. An autoimmune disorder: Your healthcare provider may order an antinuclear antibody test (ANA) to detect if there are immune proteins, called autoantibodies, in your blood. An allergy: Your healthcare provider may order a skin prick test or food allergy test to see what you may be allergic to. Leukemia: Your healthcare provider may order a bone marrow biopsy or a microscopic evaluation of your blood using a tool called flow cytometry.
Summary
White blood cells help fight infection and inflammation. A white blood cell (WBC) count measures the number of white blood cells in a sample of blood. Many conditions, including infections, medications, inflammatory diseases, and blood or bone marrow disorders, can cause an abnormal WBC count.
The WBC count is measured in a reference range of values by the number of blood cells in a cubic millimeter of blood. Test results can vary by the lab you use and how it defines a low, normal, or high range.
A WBC count isn’t specific enough to diagnose a particular disease or condition. Still, the test can provide valuable clues as to what is causing your symptoms.
A Word From Verywell
It’s important to discuss your WBC count results—and any other test you undergo—with your doctor to understand what they mean. Doing so allows you to make informed choices about your health.
It is also important not to jump to conclusions if you see a “high” or “low” notation on your WBC count results. It is only by comparing the test results to different blood test values that a healthcare provider can start narrowing down the possible causes.
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