A WBC count is a blood test to measure the number of white blood cells (WBCs) in the blood.
WBCs help fight infections. They are also called leukocytes. There are five major types of white blood cells:
- Lymphocytes (T cells and B cells)
How the Test is Performed
A blood sample is needed.
How to Prepare for the Test
Most of the time, you do not need to take special steps before this test. Tell your health care provider the medicines you are taking, including the ones without a prescription. Some drugs may change the test results.
How the Test will Feel
When the needle is inserted to draw blood, some people feel moderate pain. Others feel only a prick or stinging. Afterward, there may be some throbbing or slight bruising. This soon goes away.
Why the Test is Performed
You will have this test to find out how many WBCs you have. Your body produces more WBCs for several reasons. The most common reasons are when you have an infection or allergic reaction. You can also have more WBCs when you are under stress or have inflammation. Some people naturally have a "normal" high or low number of WBCs. An increased number of WBCs can be due to a blood cancer, such as leukemia or lymphoma.
The normal number of WBCs in the blood is 4,500 to 10,000 white blood cells per microliter (mcL).
Normal value ranges may vary slightly among different labs. Some labs use different measurements or may test different specimens. Talk to your doctor about your test results.
What Abnormal Results Mean
LOW WHITE BLOOD CELL (WBC) COUNT
A low number of WBCs is called leukopenia. A WBC count below 4500 is below normal
One type of white blood cell is the neutrophil. This type of white blood cell is important for fighting infections.
- An adult with fewer than 1700 neutrophils in a microliter of blood has a low white blood cell count.
- If there are fewer than 500 neutrophils in a microliter of blood, the risk for infection becomes even higher.
It may be due to:
- Bone marrow deficiency or failure (for example, due to infection, tumor, or abnormal scarring)
- Cancer treating drugs, or other medicines (see list below)
- Certain autoimmune disorders such as lupus
- Disease of the liver or spleen
- Radiation treatment for cancer
- Certain viral illnesses, such as mononucleosis (mono)
- Cancers that damage the bone marrow
- Very severe bacterial infections
HIGH WHITE BLOOD CELL COUNT
A high number of WBCs is called leukocytosis. It may be due to:
- Aplastic anemia
- Certain drugs or medicines (see list below)
- Cigarette smoking
- Not having a spleen, due to spleen removal
- Infections, most often those caused by bacteria
- Inflammatory disease (such as rheumatoid arthritis or allergy)
- Severe mental or physical stress
- Tissue damage (for example, burns)
There may also be less common reasons for this result.
Drugs that may lower your WBC count include:
- Anti-thyroid drugs
- Chemotherapy drugs
- Histamine-2 blockers
Drugs that may increase WBC counts include:
- Beta adrenergic agonists (for example, albuterol)
- Granulocyte colony stimulating factor
Veins and arteries vary in size from one patient to another, and from one side of the body to the other. Obtaining a blood sample from some people may be more difficult than from others.
Other risks associated with having blood drawn are slight, but may include:
- Excessive bleeding
- Fainting or feeling lightheaded
- Hematoma (blood accumulating under the skin)
- Infection (a slight risk any time the skin is broken)
Leukocyte count; White blood cell count
Vajpayee N, Graham SS, Bem S. Basic examination of blood and bone marrow. In: McPherson RA, Pincus MR, eds. Henry's Clinical Diagnosis and Management by Laboratory Methods. 22nd ed. Philadelphia, PA: Elsevier Saunders; 2011:chap 30.
Update Date 1/27/2015
Updated by: Yi-Bin Chen, MD, Leukemia/Bone Marrow Transplant Program, Massachusetts General Hospital, Boston, MA. Also reviewed by David Zieve, MD, MHA, Isla Ogilvie, PhD, and the A.D.A.M. Editorial team.