A blood differential test, 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:
It can detect abnormal or immature cells and can diagnose an infection, inflammation, leukemia, or an immune system disorder.
Your doctor may order a blood differential test as part of a routine health exam. A blood differential test is often part of a complete blood count (CBC). It’s also necessary if the results from your CBC are not within the normal range.
Your doctor may also order a blood differential test if they suspect that you have an infection, inflammation, a bone marrow disorder, or an autoimmune disease.
Your doctor will check your white blood cell levels by testing a sample of your blood. This test is often performed at an outpatient clinical laboratory. The healthcare provider at the lab will use a small needle to draw blood from your arm or hand. There’s no special preparation necessary before the test.
Once they have the sample, a laboratory specialist will put a drop of your blood on a clear glass slide and smear it to spread the blood around. Then, they will stain the blood smear 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.
The risk of complications from having your blood drawn is very slight. Some people experience mild pain or dizziness while giving a blood sample. After the test, a bruise, slight bleeding, an infection, or a hematoma (a blood-filled bump under your skin) might develop at the puncture site.
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 due to the same underlying condition.
Lab values may vary. In healthy people, the percentages of white blood cells in the sample are as follows:
- 40 to 70 percent neutrophils
- 20 to 40 percent lymphocytes
- 2 to 8 percent monocytes
- 1 to 4 percent eosinophils
- 0.5 to 1 percent basophils
If the percentage of neutrophils in your blood is too high, you might have:
- an acute infection, especially a bacterial infection
- acute stress
- eclampsia, which is a complication of pregnancy
- inflammation, such as inflammatory bowel disease or rheumatoid arthritis
- tissue injury due to trauma
- chronic leukemia
If the percentage of neutrophils in your blood is too low, you might have:
- aplastic anemia, which is a decrease in the number of blood cells produced by your bone marrow
- a severe or widespread bacterial or viral infection
- recently undergone chemotherapy or radiation therapy treatments
If there’s an increased percentage of lymphocytes in your blood, it may be due to:
- a chronic bacterial infection
- multiple myeloma, which is a cancer of the cells in your bone marrow
- a viral infection, such as mononucleosis, mumps, or measles
- lymphocytic leukemia
- lymphoma, which is a white blood cell cancer that originates in your lymph nodes
If there’s a decreased percentage of lymphocytes in your blood, it may be due to:
- bone marrow damage due to chemotherapy or radiation treatments
- HIV, tuberculosis, or hepatitis infection
- a severe infection, such as sepsis
- an autoimmune disorder, such as lupus or rheumatoid arthritis
If the percentage of monocytes in your blood is too high, it might be due to:
- chronic inflammatory disease, such as inflammatory bowel disease
- a parasitic or viral infection
- a bacterial infection in your heart
- a collagen vascular disease, such as lupus, vasculitis, or rheumatoid arthritis
- certain types of leukemia
If the percentage of eosinophils in your blood is too high, it might be due to:
- an allergic reaction
- skin inflammation, such as eczema or dermatitis
- a parasitic infection
- an inflammatory disorder, such as inflammatory bowel disease or celiac disease
- certain cancers
If the percentage of basophils in your blood is too high, it might be due to:
- a serious food allergy
If you have a persistent increase or decrease in the levels of any of the listed types of white blood cells, your doctor will likely order more tests, such as a bone marrow biopsy, to determine the underlying cause. After your doctor identifies the cause of your abnormal results, they will discuss management options with you.