A white blood cell (WBC) count is a test that measures the number of white blood cells in your body. This test is often included with a complete blood count (CBC). The term “white blood cell count” is also used more generally to refer to the number of white blood cells in your body. There are several types of white blood cells, and your blood usually contains a percentage of each type. Sometimes, however, your white blood cell count can fall or rise out of the healthy range.
WBCs, also called leukocytes, are an important part of the immune system. These cells help fight infections by attacking bacteria, viruses, and germs that invade the body. White blood cells originate in the bone marrow but circulate throughout the bloodstream. There are five major types of white blood cells:
Having a higher or lower number of WBCs than normal may be an indication of an underlying condition. A WBC count can detect hidden infections within your body and alert doctors to undiagnosed medical conditions, such as autoimmune diseases, immune deficiencies, and blood disorders. This test also helps doctors monitor the effectiveness of chemotherapy or radiation treatment in people with cancer.
An average normal range is between 3,500 and 10,500 white blood cells per microliter of blood (mcL). Infants are often born with much higher numbers of WBCs, which gradually even out as they age. According to the Mayo Clinic, these are the normal ranges of WBCs per microliter of blood by age:
|Age||White blood cells per mcL of blood|
|immediately after birth||9,000 to 30,000|
|1 to 7 days||9,400 to 34,000|
|8 to 14 days||5,000 to 21,000|
|15 days to 1 month||5,000 to 20,000|
|2 to 5 months||5,000 to 15,000|
|6 months to 1 year||6,000 to 11,000|
|2 years||5,000 to 12,000|
|3 to 5 years||4,000 to 12,000|
|6 to 11 years||3,400 to 10,000|
|12 to 15 years||3,500 to 9,000|
|adults||3,500 to 10,500|
These normal ranges can vary by lab. Another common measurement for the volume of blood is cubic millimeter, or mm3. A microliter and cubic millimeter are the same amount.
The types of cells that make up WBCs usually fall within a normal percentage of your overall white blood cell count.
The normal percentages of the types of WBCs in your overall count are usually in these ranges:
|Type of WBC||Normal percentage of overall WBC count|
|neutrophil||45 to 75 percent|
|lymphocyte||20 to 40 percent|
|eosinophil||less than 7 percent|
|monocyte||1 to 10 percent|
|basophil||less than 3 percent|
Higher or lower numbers of WBCs than normal can be a sign of an underlying condition. Having a higher or lower percentage of a certain type of WBC can also be a sign of an underlying condition.
Symptoms of an abnormal count
The symptoms of a low WBC count include:
High WBC counts don’t often cause symptoms, although the underlying conditions causing the high count may cause their own symptoms.
The symptoms of a low white blood cell count may prompt your doctor to recommend a WBC count. It’s also normal for doctors to order a complete blood count and check your WBC count during an annual physical examination.
A healthcare provider or lab technician will draw blood to check your WBC count. This blood sample is taken either from a vein in your arm or a vein on the back of your hand. It only takes a couple of minutes to draw your blood, and you may experience minor discomfort. The healthcare provider will clean the needle site to kill any germs and then tie an elastic band around the upper section of your arm. This elastic band helps the blood fill your vein, making it easier for the blood to be drawn.
The healthcare provider slowly inserts a needle into your arm or hand and collects the blood in an attached tube. The provider then removes the elastic band from around your arm and slowly removes the needle. The technician will apply gauze to the needle site to stop the bleeding.
Healthcare providers use a different technique when drawing blood from young children and infants. With them, providers first puncture the skin with a lancet (a pricking needle) and then use a test strip or a small vial to collect the blood. Results are sent to a lab for review.
Having your blood drawn is a simple procedure, and complications are extremely rare. It can be difficult to take blood from people with small veins. The lab technician may be unable to locate a vein, or once the needle is inside the arm or hand, they may have to move the needle around in order to draw blood. This can cause a sharp pain or a stinging sensation.
Rare complications include:
- infection at the needle site
- excessive bleeding
- lightheadedness or fainting
- bleeding underneath the skin (hematoma)
A WBC count requires no specific preparation. You simply schedule an appointment with your doctor or set up an appointment at a local medical laboratory. Certain medications can interfere with your lab results and either lower or increase your WBC count.
The drugs that may affect your test results include:
- chemotherapy medication
Prior to having your blood drawn, tell your doctor about all prescription and nonprescription medications that you’re currently taking.
Abnormal test results are classified by numbers that are higher or lower than the normal range for your age.
A low or high WBC count can point to a blood disorder or other medical condition. To identify the exact cause of a high or low WBC count, your doctor will take several factors into consideration, such as your list of current medications, symptoms, and medical history.
Leukopenia is the medical term used to describe a low WBC count. A low number can be triggered by:
- autoimmune disorders
- bone marrow disorders/damage
- severe infections
- liver and spleen diseases
- radiation therapy
- some medications, such as antibiotics
Leukocytosis is the medical term used to describe a high WBC count. This can be triggered by:
- infections such as tuberculosis
- tumors in the bone marrow
- inflammatory conditions, such as arthritis and bowel disease
- tissue damage
- some medications, such as corticosteroids
After diagnosing the cause of a high or low WBC count and recommending a treatment plan, your doctor will periodically recheck your white blood cells. If your white blood cell count remains high or low, this can indicate that your condition has worsened. Your doctor may adjust your treatment. If your WBC count shows a normal range, this usually indicates that the treatment is working.