Test Quick Guide

A WBC is a test that measures the number of leukocytes in the blood. Leukocytes are an important part of the immune system that help defend against infections and diseases.

A WBC test is most often conducted at the same time as other measurements in a complete blood count (CBC), a common test used to diagnose and monitor a wide variety of health conditions.

A WBC count can help diagnose infections, inflammation, and other health conditions that affect WBC. If the results of a WBC count are outside of the healthy range, additional tests are performed to determine the cause.

A related test, called a WBC differential, measures the percentage and absolute number of each type of WBC in the blood and may also be included with a CBC.

About the Test

Purpose of the test

The purpose of a WBC count is to determine whether the total number of WBC is within a healthy range. This test is often performed alongside other blood testing, such as a CBC, which also measures other contents of the blood like red blood cells and platelets.

Knowing the WBC count can help diagnose infections, conditions that cause inflammation, allergic reactions, and cancers of the blood and lymphatic system. A WBC count is also used to monitor your response to certain medical treatments that can affect the immune system including chemotherapy and medications that suppress the immune system.

What does the test measure?

A WBC count measures the total number of WBCs contained in a sample of blood. WBC, also called leukocytes, are an important part of the immune system. Made in the bone marrow, WBC help defend the body against infections and disease. There are five types of WBC, each supporting the immune system in a different way.

The WBC count is usually expressed as thousands of cells per microliter (cells/μL). Around 100 billion WBC are produced each day in the bone marrow. As they mature, WBC can be found in blood and the lymphatic system. There are five types of WBC:

  • Basophils
  • Eosinophils
  • Lymphocytes
  • Monocytes
  • Neutrophils

A WBC count measures the total amount of all kinds of WBC. If a doctor needs information about the number of individual types of WBC, this information is provided in the WBC differential test.

When should I get a WBC?

A WBC count is a standard component of a CBC. A doctor may order a CBC in many situations, including:

  • During a routine doctor visit or checkup
  • While you are getting medical treatment that can affect your immune system and blood cell counts
  • For ongoing monitoring of chronic health issues that can affect blood counts, including chronic bone marrow disease

Your doctor may also order a CBC if you have certain symptoms, such as:

  • Excessive tiredness or weakness
  • Weight loss
  • Fever or other symptoms of infection
  • Unexpected bleeding or bruising
  • Signs of cancer

A doctor or other health care provider can share additional information about whether a CBC may be appropriate for your situation and how a WBC count is used to understand your health.

Finding a WBC

How can I get a WBC test?

A WBC count is typically prescribed by a health care provider and conducted at a medical facility like a doctor’s office, clinic, or hospital. You can order a WBC test online as part of a CBC test.

Can I take the test at home?

A CBC that includes a WBC count is typically performed in a medical setting. However, the test is also available as an at-home self-collection test.

This type of testing involves purchasing a test kit online and collecting a sample of blood at home by pricking your finger with a very small needle. After placing several drops of blood on a special test paper, mail your sample to a laboratory for testing. Results of self-collection tests may be available within a few days after the lab receives your test sample.

How much does the test cost?

The cost of a WBC count depends on several factors, including where the test is conducted, if any other blood tests are being done simultaneously, and whether you have a health insurance plan.

For more information about the cost of testing, talk to your doctor or the medical facility where the test is being conducted.

Taking a WBC Test

A WBC count requires a sample of blood. Typically, the blood sample is drawn from a vein in your hand or on the inside of your elbow.

Before the test

Although no preparation is usually required before a WBC count, it is important to talk to your doctor about any medications that you are currently taking because some medications can affect your test result.

During the test

To collect a blood sample, a doctor or other health care provider will begin by locating a vein and cleaning around the puncture site. To locate the vein, a band may be tied around your upper arm to increase blood flow.

A needle is then inserted into your vein, and blood is drawn into an attached test tube. You may experience slight stinging when the needle enters your skin, but any discomfort is temporary. The process of collecting a blood sample usually takes only a few minutes.

After the test

After your blood is collected for testing, you may be given a piece of gauze or cotton to put over the site where the needle was inserted. A bandage may be placed on your arm to reduce any bleeding, bruising, or swelling. The health care provider will tell you how long to keep the bandage in place.

Having blood drawn is a routine and safe procedure. As with any medical test, there are small risks of complications such as bruising, infection, and feeling lightheaded.

WBC Test Results

Receiving test results

You will likely receive your WBC count as part of the results of a CBC. Results may be shared during a follow-up visit, and a test report may be available through your online medical record. The results of a CBC, including the WBC count, are usually available within a few business days.

Interpreting test results

A CBC test report will include your WBC count as well as other measurements and the laboratory’s normal reference ranges, which show the levels that the laboratory expects to find if you are healthy.

Your WBC count will be written on your test report as WBCs per microliter (cells/μL). If you are healthy, the reference range for WBC count may vary from lab to lab, so it is important to discuss the meaning of your results with a health care provider.

A high WBC count is also called leukocytosis and may be caused by many conditions, including:

  • Infection
  • Smoking cigarettes
  • Inflammation
  • Injuries that damage tissue, such as burns
  • Allergies like asthma or hay fever
  • Cancer, including leukemia or lymphoma
  • Pregnancy
  • Certain medications

A low WBC count is also called leukopenia and may be due to health issues such as:

  • A problem with the production of WBCs in the bone marrow
  • Autoimmune disorders
  • Health conditions affecting the liver or spleen
  • Cancer or cancer treatment
  • Psychological stress
  • Certain medications

A WBC count alone typically cannot diagnose any of these conditions, but abnormal levels of leukocytes may provide an indication of an underlying health issue.

Although the full results from a CBC may provide helpful information about potential causes of an abnormal WBC count, follow-up tests are often needed. For this reason, it is important to discuss questions about your WBC count with your doctor.

It may be helpful to ask your health care provider the following questions about your WBC count:

  • What is my WBC count?
  • Do other parts of the CBC provide information about the reason for my abnormal WBC count?
  • Do I need any follow-up tests? If so, what tests are appropriate?



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