Understanding the WBC (white blood cell) count

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.

Having a higher or lower number of WBCs than normal may indicate 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.

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:

Infants are often born with much higher numbers of WBCs, which gradually even out as they age.

According to the University of Rochester Medical Center (UMRC), these are the normal ranges of WBCs per microliter of blood (mcL):

Age rangeWBC count (per mcL of blood)
newborns9,000 to 30,000
children under 26,200 to 17,000
children over 2 and adults5,000 to 10,000

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 equal the same amount.

The types of cells that make up WBCs usually fall within a normal percentage of your overall WBC count.

The normal percentages of the types of WBCs in your overall count are usually in these ranges, according to the Leukemia & Lymphoma Society (LLS):

Type of WBCNormal percentage of overall WBC count
neutrophil55 to 73 percent
lymphocyte20 to 40 percent
eosinophil1 to 4 percent
monocyte2 to 8 percent
basophil0.5 to 1 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.

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 WBC count may prompt your doctor to recommend a WBC count. It’s also normal for doctors to order a CBC and check your WBC count during an annual physical examination.

A healthcare provider or lab technician needs to 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 first cleans the needle site to kill any germs and then ties 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. Finally, the technician applies gauze to the needle site to stop the bleeding.

Healthcare providers use a different technique when drawing blood from young children and infants: 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:

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:

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:

Leukocytosis is the medical term used to describe a high WBC count. This can be triggered by:

After diagnosing the cause of a high or low WBC count and recommending a treatment plan, your doctor will periodically recheck your WBCs.

If your WBC 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.