Blood Differential

Blood Differential
Smiling medical team standing together outside a hospital

A blood differential test measures the amount of each type of white blood cell (WBC) that you have in your body. White blood cells (leukocytes) are part of your immune system, a network of cells, tissues, and organs that work together to protect you from infection. There are five different types of white blood cells:

  • Neutrophils are the most common type of white blood cell. They are your body’s main defense against infection when bacteria, viruses, or other germs enter your body.
  • Lymphocytes include two main types of white blood cells: B cells and T cells. B cells fight off invadingviruses, bacteria, or toxins. Certain T cells can target and destroy your body’s own cells, such as cancer cells and cells that have been infected by viruses.
  • Monocytes kill bacteria, viruses, and other germs that may make you sick. They also boost your body’s immune response and clear away dead cells.
  • Eosinophils defend against parasites and infections. They are also involved in allergies and help control inflammation (swelling and redness).
  • Basophils release enzymes during allergic reactions and asthma attacks.

However, your test results may have more than five numbers. For example, the lab may list the results as counts as well as percentages.

Other names for a blood differential test: Complete blood count (CBC) with differential, Differential, White blood cell differential count, Leukocyte differential count

What is it used for?

A blood differential test is often part of a general physical exam. Because the five types of white blood cell do different jobs, measuring them separately can give your health care provider important information about your health.

The test can also help diagnose a variety of medical conditions, such as:

  • Infections
  • Autoimmune diseases
  • Inflammatory diseases
  • Leukemia and other types of cancer

Why do I need a blood differential test?

A blood differential test is used for many reasons. Your provider may have ordered the test to:

  • Monitor your overall health or as part of a routine checkup.
  • Diagnose a medical condition when you have symptoms. For example, if you are feeling unusually tired or weak, or have unexplained bruising or other symptoms, this test may help uncover the cause.
  • Keep track of an existing blood disorder or related condition.

What happens during a blood differential test?

A health care professional will take a blood sample from a vein in your arm, using a small needle. After the needle is inserted, a small amount of blood will be collected into a test tube or vial. You may feel a little sting when the needle goes in or out. This usually takes less than five minutes.

Will I need to do anything to prepare for the test?

No special preparation is necessary.

Are there any risks to the test?

There is very little risk to having a blood test. After the test, some people experience mild pain, dizziness, or bruising. These symptoms usually go away quickly.

What do the results mean?

There are many reasons your blood differential test results may be higher or lower than normal. For example, a high white blood cell count may mean you have an infection, an immune disorder, leukemia, or an allergic reaction. A low count may be caused by bone marrow problems, reactions to medicines, or cancer.

But abnormal results don’t always mean you have a condition that needs medical treatment. Factors such as exercise, diet, alcohol level, medicines, and even a woman’s menstrual period can affect the results.

If your results seem abnormal, your provider may order more specific tests to help figure out the cause. To learn what your results mean, talk with your provider.

Is there anything else I need to know about a blood differential test?

Use of certain steroids may increase your white blood cell count, which can lead to an abnormal result in your blood differential test.

Courtesy of MedlinePlus from the National Library of Medicine.