How Does A Blood Differential Test Help?

blood differential test
blood differential test

If your doctor has ordered a blood differential test for you and you’re wondering what it’s all about, look no further. We’ve got all the info you need. The blood differential test is used to check the percentage of each kind of white blood cell that is present in your blood. It can also tell you if there are immature cells or abnormal cells present.1 Since white blood cells (or leukocytes) form a part of the immune system and help to fight infections an increase in their numbers can indicate the presence of an infection.

There are five main kinds of white blood cells – neutrophils, basophils, eosinophils, lymphocytes, and monocytes – and each kind has a slightly different task. Neutrophils defend us by destroying infection-causing microorganisms. Eosinophils kill parasites and play a role in allergic reactions which are meant to defend us from harmful foreign substances; basophils too have a role in the development of allergic reactions. Meanwhile, monocytes enter tissues and become macrophages which kill microorganisms and remove damaged, old, and dead cells. Lymphocytes use antibodies to stop germs and also destroys the body’s cells if they’ve been compromised. These white blood cells are able to retain a memory of the bacteria and viruses that have invaded your body too and can recognize them when they encounter them again. 2


The white blood cell differential test is generally run as part of the full blood count (FBC) test which checks the kinds and numbers of cells in the blood, including white blood cells, red blood cells, and platelets.3 4 The full blood count test can be done as a part of a routine check-up. It may also be run if you show signs of fatigue, fever, weight loss, infection, bruising, weakness, bleeding, or any signs of cancer and to monitor conditions like chronic kidney disease which can change your blood count results.5

How Is The Test Done?

First, your blood sample is taken. Then a lab specialist smears a drop of your blood on a glass slide and stains it with a dye that can help to tell the difference between the many kinds of white blood cells. A health care professional counts the number of each kind cell either manually or uses a machine to do it to check if they are in proper proportion to each other.6


Why Is It Run?

The white blood cell differential test is used to diagnose anemia and infections and can also identify some kinds of leukemia (cancer of blood-forming organs usually the bone marrow) and lymphoma (cancer of the immune cells). It can be helpful in monitoring these conditions and check if treatments for them are working too. It can also evaluate the body’s ability to fight infection, including HIV-AIDS and determine the severity of drug and allergic reactions as well as infections.7 8

What Do The Results Mean?

Normally, neutrophils form 40 to 60 % of white blood cells; lymphocytes form 20 to 40% monocytes form 2 to 8%; eosinophils form 1 to 4%; basophils form 0.5 to 1%, and band (young neutrophil) form 0 to 3%. An abnormal increase in one type of white blood cell and consequent percentage decrease in other types can indicative of infection, inflammation, diseases like leukemia etc. Let’s take a look at what an abnormal value for the different kinds of white blood cells might mean:



An increase in their percentage may be because of:

  • Acute infection or stress
  • Eclampsia, a condition where a woman who had a complication of pregnancy known as preeclampsia, which is characterized by high blood pressure, experiences seizures or coma.9
  • Gout, a kind of arthritis where uric acid accumulates in the blood and causes inflammation of the joints.10
  • Myelocytic leukemia, a cancer that begins in the bone marrow, which is the tissue that helps in formation of all blood cells.11
  • Rheumatoid arthritis which is a chronic condition characterized by inflammation of the joints and tissues.
  • Rheumatic fever, which is a disease that may occur after an infection by group A streptococcus bacteria (for example, scarlet fever or strep throat). This germ can cause the immune system to attack healthy tissues.12
  • Thyroiditis which is caused by a reaction of the immune system against the thyroid gland. It can cause reduced thyroid function.13
  • Trauma

A decrease in their percentage maybe because of:

  • Aplastic anemia, a blood disorder in which the body’s bone marrow doesn’t make enough new blood cells.14
  • Chemotherapy, exposure to radiation or radiation therapy
  • Influenza (flu)
  • Viral or bacterial infection


An increase in their percentage maybe because of:

  • Chronic bacterial infection
  • Infectious hepatitis which is characterized by inflammation and swelling of the liver
  • Infectious mononucleosis, a viral infection that causes a sore throat, fever, and swollen lymph glands.15
  • Lymphocytic leukemia, a cancer of white blood cells (known as lymphoblast).
  • Multiple myeloma, a blood cancer that starts in the bone marrow.16
  • Viral infections like measles or mumps

A decrease in their percentage maybe because of:

  • Chemotherapy, radiation therapy, or exposure to radiation
  • HIV infection
    • Leukemia
    • Sepsis, which is a severe response to germs shown by the body17
    • The use of steroids


An increase in their percentage maybe because of:

  • Leukemia
  • Infection by a parasitic
  • Chronic inflammation
  • Tuberculosis
  • Viral infections like measles or mumps

A decrease in their percentage maybe because of:

  • A bloodstream infection
  • Chemotherapy
  • A bone marrow disorder
  • Certain skin infections
  • A human papillomavirus (HPV) infection in the genitals18


An increase in their percentage maybe because of:

  • Addison disease, which is a disorder of the adrenal glands.19
  • Allergic reaction
  • Chronic myelogenous leukemia, which is a cancer that starts in the bone marrow.
  • Collagen vascular disease where the body’s immune system attacks healthy tissues.20
  • Hypereosinophilic syndromes where you see high numbers of eosinophils which make their way into various tissues causing inflammation and organ dysfunction.21
  • Parasitic infection

A decrease in their percentage maybe because of:

  • Cushing syndrome, which is characterized by high levels of the hormone called cortisol.22
  • Bloodstream infections
  • The use of steroids23


An increase in their percentage maybe because of:

  • The removal of your spleen.
  • Collagen vascular disease
  • Allergic reaction
  • Chronic myelogenous leukemia
  • Myeloproliferative disease, which is a group of conditions that cause blood cells to grow abnormally in the bone marrow.24
    • Chickenpox

A decrease in their percentage maybe because of:

  • Cancer
  • Acute infection or severe injury25

But do keep in mind that factors like stress, physical activity, long-term exposure to toxic chemicals like insecticides, smoking etc. can also cause changes in your white blood differential values. And your doctor is best suited to interpret the results of your test.26

Risk Factors

There is very little risk associated with having your blood taken. But there’s always a slight risk of infection any time the skin is broken, and some people may experience excessive bleeding or feel lightheaded.27