White Blood Cell (WBC) Differential

How is the test used?

The white blood cell differential is often used as part of a complete blood count (CBC) as a general health check. (This testing is sometimes called CBC with differential or CBC with diff for short.)

A WBC differential may be used to help diagnose the cause of a high or low white blood cell (WBC) count results seen on a CBC. It may also be used to help diagnose and/or monitor other diseases and conditions that affect one or more different types of WBCs. Some examples of these conditions include:

• Infections caused by bacteria, viruses, fungi or parasites
• Inflammation
• Allergies, asthma
• Immune disorders (e.g., autoimmune disorders, immune deficiency)
• Leukemia (e.g., chronic myeloid leukemia, chronic lymphocytic leukemia)
• Myelodysplastic syndrome
• Myeloproliferative neoplasms (e.g., myelofibrosis)

When is it ordered?

You may have a complete blood count (CBC) and WBC differential (CBC with diff) when you go for a routine health exam.

A differential is typically included as part of the CBC and is particularly important when you have general signs and symptoms of an infection and/or inflammation, such as:

• Fever, chills
• Body aches, pain
• Headache
• A variety of other signs and symptoms, depending on the site of suspected infection or inflammation

Testing may be performed when you have signs and symptoms that your healthcare provider thinks may be related to a blood and/or bone marrow disorder, autoimmune disease or other immune disorder.

If a differential is not done at the same time as a CBC, it may be ordered when results from the CBC are not within the reference ranges.

What does the test result mean?

WBC differential results indicate the number and/or the percentage of each type of white blood cell that is present in your sample of blood at the time of the test.

Results of a differential are usually reported as absolute values of the five types of WBCs and/or may be reported as a percent of the total number of WBCs. Absolute values are calculated by multiplying the total number of WBCs by the percentage of each type of white cell. In adults, neutrophils typically make up the highest number of WBCs, followed by lymphocytes, then monocytes, eosinophils and basophils. In young children, lymphocytes are often more numerous than neutrophils.

When interpreting your results of a differential, your healthcare provider will consider several factors, including your signs and symptoms and medical history as well as how high or low each type of WBC is and whether the increase or decrease persists. 

• A number of factors can cause a temporary rise or drop in the number of any one type of WBC. A persistent increase or decrease will usually prompt your healthcare practitioner to order more testing to determine the cause.
• A result that is barely outside the reference range may or may not be significant for you while a large rise or drop in one or more types of WBCs usually prompts more testing.

The following table gives some examples of what results might mean:

Possible Causes of High and Low WBC Differential Results

¹ from Wintrobe's Clinical Hematology. 14th ed. Greer J, editor. Philadelphia, PA: Wolters Kluwer: 2019.

In certain cases, immature and/or abnormal cells may be present in the blood and may be detected with a differential. Immature cells include metamyelocytes, myelocytes, promyelocytes, and/or blasts. Additional testing (e.g., bone marrow biopsy) may be necessary.

My complete blood count (CBC) report includes a result for immature granulocytes (IG). What are they?

Some automated hematology analyzers report the total number of immature granulocytes (IG) present in a person's blood sample. Immature granulocytes are white blood cells that have not fully developed before being released from the bone marrow into the blood. They may include metamyelocytes, myelocytes, and promyelocytes. These cells are normally only present in the bone marrow because they are precursors of neutrophils, the predominant type of white cells in blood. The presence of immature granulocytes in the blood may occur in various diseases, such as infection or a blood cancer, and thus will often prompt further investigation, which may include additional laboratory testing.

Can a white blood cell (WBC) differential be performed on samples other than blood?

Yes. WBC differentials, along with WBC counts, may be performed on many different types of body fluids. A common reason that this is done is to more directly assess one area of the body that may be infected or inflamed. For example, if meningitis is suspected, then a WBC count plus differential may be performed on a sample of cerebrospinal fluid (CSF). Many other examples are listed in the article on Body Fluid Analysis.

If I have an abnormal result on my WBC differential, what other tests might my healthcare provider order?

Other general tests to check your health may include a comprehensive metabolic panel (CMP). Depending on your signs, symptoms, medical history, physical exam and suspected condition, your healthcare provider may choose to order a variety of other tests. A few general examples include:

• Bacterial infection: a culture of the affected area (e.g., urine culture, sputum culture, blood culture), strep test

• Viral infection: tests for mononucleosis, Epstein-Barr virus

• Inflammation: C-reactive protein, erythrocyte sedimentation rate (ESR)

• Autoimmune diseases: Antinuclear antibody

• Allergies: Allergy tests

• Leukemia or other bone marrow disorders: Bone marrow biopsy, immunophenotyping, chromosome analysis

My report mentions a "left shift." What does this mean?

A "left shift" is a phrase used to note that there are young/immature white blood cells present. Most commonly, this means that there is an infection or inflammation present and the bone marrow is producing more WBCs and releasing them into the blood before they are fully mature. This is a natural immune response to infection and inflammation.