Blood Differential
A blood differential test measures the amount and percentage of each type of white blood cell in your blood to help diagnose or monitor infections and immune system conditions.
What is a blood differential test?
A blood differential test measures the amount of each type of white blood cell (WBC) that you have in your blood. This test can help diagnose or monitor an infection or condition that affects your immune system.
White blood cells are also called leukocytes and WBCs. They are a type of blood cell that is made in your bone marrow and found in your blood and lymph tissue. When you are injured or sick, your white blood cells travel through your bloodstream and tissues to fight off the infection or disease. There are five different types of white blood cells:
- Neutrophils: 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 B cells and T cells. B cells fight off invading viruses, bacteria, or toxins, while certain T cells can target and destroy your body's own cells, such as cancer cells and cells infected by viruses.
- Monocytes: Kill bacteria, viruses, and other germs, 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.
- Basophils: Release enzymes during allergic reactions and asthma attacks.
A blood differential test measures the amount and/or percentage of each type of white blood cell. Another test called a white blood count (WBC) measures the total number of these cells in your blood.
What is it used for?
A blood differential test is often part of a routine checkup. Because the five types of white blood cell do different jobs, measuring them separately provides important information about your health. The test can help diagnose a variety of medical conditions, such as:
- Infections
- Autoimmune diseases such as rheumatoid arthritis
- Leukemia and other types of cancer
Why do I need a blood differential test?
Your provider may order the test to:
- Monitor your overall health or as part of a routine checkup.
- Diagnose the cause of your symptoms or an abnormal WBC count from another blood test.
- Monitor 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. A small amount of blood is 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.
What do the results mean?
Your blood differential test results may be higher or lower than normal for many reasons. Conditions that may cause a high white blood cell count (leukocytosis) include infections, autoimmune or inflammatory disorders, leukemia or Hodgkin disease, allergic reactions, and certain steroids. Conditions that may cause a low white blood cell count (leukopenia) include bone marrow diseases, chemotherapy, certain medicines, cancer, and HIV.
Abnormal results do not always mean you have a condition requiring treatment. Other factors that may affect your results include physical injury, extreme stress, smoking, and alcohol use.