A blood differential (also called a white blood cell count differential) measures the number of each of the five types of white blood cells present in your blood:

    • neutrophils
    • lymphocytes
    • monocytes
    • eosinophils
    • basophils

    It can detect abnormal or immature cells and can be used to diagnose an infection, inflammation, leukemia, or an immune system disorder.

    Why Is a Blood Differential Performed?

    Your doctor may order a blood differential as part of a routine health exam. A blood differential is often performed as part of a complete blood count (CBC), or if the results from a CBC are not within the normal range.

    Your doctor may also order a blood differential if he or she suspects that you have an infection, inflammation, a bone marrow disorder, or an autoimmune disease.

    How Is a Blood Differential Performed?

    Your doctor will check your white blood cell levels by testing a sample of your blood. Usually you will be asked to go to an outpatient clinical laboratory to have your blood sample taken. The healthcare provider at the lab will use a small needle to draw blood from your arm or hand. No special preparation is necessary before the test.

    Once the sample has been taken, a laboratory specialist will put a drop of your blood on a clear glass slide and smear it to spread the blood around. Then the blood smear will be stained with a dye that helps to differentiate among the different types of white blood cells in the sample. The lab specialist will then count the number of each type of white blood cell (either by hand or using a computer).

    What Complications Are Associated with a Blood Differential?

    The risk of complications from having your blood drawn is very slight. Some people experience mild pain or dizziness while having ablood sample taken. After the test, a bruise, slight bleeding, an infection, or a hematoma (a blood-filled bump under your skin) could develop at the puncture site.

    What Do the Test Results Mean?

    Food, exercise, and stress can affect your white blood cell count. An abnormal increase in one kind of white blood cell can cause a decrease in another kind, so both abnormal results can be caused by the same underlying condition.

    In healthy people, the percentages of white blood cells in the sample are as follows:

    • neutrophils: 40 to 60 percent
    • lymphocytes: 20 to 40 percent
    • monocytes: 2 to 8 percent
    • eosinophils: 1 to 4 percent
    • basophils: 0.5 to 1 percent

    You may have too high a percentage of neutrophils in your blood if you have:

    You may have too low a percentage of neutrophils in your blood if you have:

    • aplastic anemia (a decrease in the number of blood cells produced by your bone marrow)
    • been undergoing chemotherapy treatments
    • a severe or widespread bacterial or viral infection

    An increased percentage of lymphocytes in your blood may be caused by:

    A decreased percentage of lymphocytes in your blood may be caused by:

    • bone marrow damage due to chemotherapy or radiation treatments
    • HIV, tuberculosis, or hepatitis infection
    • leukemia
    • a severe infection (e.g. sepsis)
    • an autoimmune disorder (e.g. lupus or rheumatoid arthritis)

    The percentage of monocytes in your blood may be too high if you have:

    • a chronic inflammatory disease (e.g. inflammatory bowel disease)
    • a parasitic or viral infection
    • a bacterial infection in your heart
    • a collagen vascular disease (e.g. lupus, vasculitis, or rheumatoid arthritis)
    • certain types of leukemia

    You may have too high a percentage of eosinophils in your blood if you have:

    The percentage of basophils in your blood may be too high if you have:

    • a serious food allergy
    • inflammation
    • leukemia

    If you have a persistent increase or decrease in the levels of any of these types of white blood cells, your doctor will likely order more tests, such as a bone marrow biopsy, to determine the underlying cause. Once the cause of your abnormal results has been identified, you doctor will discuss management options with you.