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To help determine the cause of abnormal results on a white blood cell (WBC) count; to help diagnose and/or monitor an illness affecting your immune system, such as an infection or inflammatory condition, or cancers that affect your white blood cells, such as leukemia or lymphoma
When you have a complete blood count (CBC) done as part of a routine health examination; when results of a CBC fall outside the reference range; when you have signs and symptoms related to a condition affecting white blood cells, such as infection, inflammation, or cancer; when you are receiving treatment that is known to affect WBCs, such as chemotherapy
A blood sample drawn from a vein or blood collected by a pricking a fingertip (fingerstick) or the heel of an infant (heelstick)
White blood cells (WBCs), also called leukocytes, are cells that circulate in the blood and the lymphatic system that help protect the body against infections. They are an important part of the body's immune system and also have a role in inflammation, allergies, and protection against cancer. A WBC differential categorizes the numbers of each of the different types of WBCs in sample of your blood.
There are five main types of white blood cells, each with different functions. The differential shows if:
This information is helpful in diagnosing specific types of illnesses that affect the immune system and the bone marrow.
A differential may be performed along with or following a complete blood count (CBC), a test often used as a general health check, or it may be performed in follow-up to abnormal results on a CBC. Most often, a differential is performed on an automated blood analyzer. Occasionally, it is performed manually by a trained laboratory professional who examines a blood smear using a microscope.
Types of White Blood Cells
The bone marrow produces five main types of WBCs, neutrophils, lymphocytes, monocytes, eosinophils, and basophils.
What does a differential tell you?
A WBC differential can give clues about your condition or what is causing a low or high WBC count. When there is an infection or an inflammatory process somewhere in the body, the bone marrow produces more WBCs, releasing them into the blood. Depending on the cause of infection or inflammation, one particular type of WBC may be increased as opposed to other types. As the condition resolves, the bone marrow produces fewer of that type of WBC and the number drops back to normal levels.
In addition to infections and inflammation, there are a variety of conditions that can affect the production of WBCs by the bone marrow or their survival in the blood, resulting in either increased or decreased numbers. The differential, along with the other components of the CBC, alerts the healthcare provider to possible health issues. Results are often interpreted along with additional tests such as a blood smear exam, which can show the presence of abnormal and/or immature WBCs.
In a few serious diseases, some immature forms of the cells are released from the bone marrow into the circulation and may be detected by the WBC differential. This may occur with bacterial infection, leukemia, myelodysplastic syndrome, or myeloproliferative neoplasms, for example. Some immature cells that may be detected include metamyelocytes, myelocytes, promyelocytes, and/or blasts.
If results indicate a problem, a wide variety of other tests may be performed in order to help determine the cause. A healthcare provider will typically consider your signs and symptoms, medical history, and results of a physical examination to decide what other tests may be necessary. For example, as needed, a bone marrow biopsy might be performed because that is where WBCs normally are produced and where they mature.
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:
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:
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.
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.
The following table gives some examples of what results might mean:
|Type of WBC||Reference Range2||Examples of causes of a high count||Examples of causes of a low count|
|Neutrophils (Absolute neutrophil count, percent neutrophils)||
Absolute count (per microliter):
Mean number fraction: 0.56
Absolute count X 109 per liter:
|Known as neutrophilia
||Known as neutropenia
|Lymphocytes (Absolute lymphocyte count, percent lymphocytes||
Mean number fraction: 0.34
|Known as lymphocytosis||Known as lymphopenia or lymphocytopenia
|Monocytes (Absolute monocyte count, percent monocytes)||
Mean number fraction 0.04
|Known as monocytosis
||Known as monocytopenia
Usually, one low count is not medically significant.
Repeated low counts can indicate:
|Eosinophils (Absolute eosinophil count, percent eosinophils)||
Mean number fraction 0.027
|Known as eosinophilia
||Known as eosinopenia
This is often difficult to determine because numbers are normally low in the blood. One or an occasional low number is usually not medically significant.
|Basophils (Absolute basophil count, percent basophils)||
Mean number fraction 0.030
|Known as basophilia
||Known as basopenia
As with eosinophils, numbers are normally low in the blood; usually not medically significant.
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.
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.
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.
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:
• Autoimmune diseases: Antinuclear antibody
• Allergies: Allergy tests
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.
Sources Used in Current Review
2015 review performed by Nicole Ziegler, MT (ASCP) and the Lab Tests Online Editorial Review Board.
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