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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
As part of a complete blood count (CBC), when you have a routine health examination; when results of a CBC fall outside the reference range; when you have any number of signs and symptoms that may be 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 in your arm or by a fingerstick (children and adults) or heelstick (infants)
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, allergic responses, and protection against cancer. A WBC differential totals the number of each of the different types of WBCs in a person's sample of blood.
There are five types of white blood cells, each with different functions. The differential reveals if the cells are present in normal proportion to one another, if the number of one cell type is increased or decreased, or if abnormal and/or immature cells are present. This information is helpful in diagnosing specific types of illnesses that affect the immune system and the bone marrow.
A differential may be performed in conjunction with 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 but also may be performed manually by a trained laboratorian who examines a blood smear under a microscope. The values are typically reported as absolute numbers of cells but may be expressed as the relative percentages of the total number of WBCs.
White blood cells develop from precursor cells produced in the bone marrow. The five different types of WBCs include:
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 production of that type of WBC subsides and the number drops to normal levels again.
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 in conjunction with additional tests such as a blood smear review, which can reveal the presence of abnormal and/or immature populations of 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, bone marrow involvement by solid tumor, 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 an individual's 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 will be performed to evaluate the bone marrow status.
A blood sample is drawn from a vein in the arm or from a fingerstick (for children and adults) or heelstick (for infants).
No test preparation is needed.
The white blood cell differential is often used as part of a complete blood count (CBC) as a general health check. It may be used to help diagnose the cause of a high or low white blood cell (WBC) count, as determined with 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.
The five types include: neutrophils, lymphocytes, monocytes, eosinophils and basophils. (For more details on these, see the "What is being tested?" section.)
The differential totals the number of each type and determines if the cells are present in normal proportion to one another, if one cell type is increased or decreased, or if immature cells are present. This information is useful in helping to diagnose the specific cause of an illness, such as:
Some diseases trigger a response by the immune system that causes an increase in certain types of WBCs. A differential may give clues to the specific cause of that immune response. For example, it may help determine whether an infection is caused by bacteria or by viruses.
Other conditions affect the production of certain WBCs by the bone marrow or their survival in the circulation, resulting in either an increase or decrease in their number. A differential informs the healthcare provider as to which type of WBC is low or high.
An abnormal differential result may be followed by other tests such as a blood smear, bone marrow biopsy, chromosome analysis, or immunophenotyping (e.g., flow cytometry). These tests can reveal the presence of abnormal and/or immature populations of WBCs.
The differential is often performed as part of the complete blood count (CBC), which may be ordered at the time of a routine health exam.
A differential may be included as part of the CBC when someone has general signs and symptoms of an infection and/or inflammation, such as:
Testing may be performed when there are signs and symptoms that the 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.
The results indicate the number and/or the percentage of each type of white blood cell that is present in a person's sample of blood.
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. This information can aid in diagnosing illness and monitoring therapy. Neutrophils typically make up the highest number of WBC, followed by lymphocytes, then monocytes, eosinophils and basophils.
Care must be taken when interpreting the results of a differential. A healthcare provider will consider an individual's signs and symptoms and medical history as well as the degree to which the cells are increased or decreased. A number of factors can cause a transient rise or drop in the number of any one type of cell. A persistent increase or decrease will usually prompt further testing to determine the cause.
The following table gives some examples as to what the results of a differential may indicate:
|Type of WBC||Abbreviations||Examples of causes of a high count||Examples of causes of a low count|
|Neutrophils (Absolute neutrophil count, percent neutrophils)||
Neu, Polys, PMNs, ANC, % Neu
|Known as neutrophilia
||Known as neutropenia
|Lymphocytes (Absolute lymphocyte count, percent lymphocytes||
Lymphs, lym, ly, ALC, % lymphs
|Known as lymphocytosis||Known as lymphopenia or lymphocytopenia
|Monocytes (Absolute monocyte count, percent monocytes)||
Monos, AMC, % monos
|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)||
Eos, AEC, % eos
|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)||
Baso, ABC, % baso
|Known as basophilia
||Known as basopenia
As with eosinophils, numbers are normally low in the blood; usually not medically significant.
In certain cases, immature and/or abnormal forms of the cells may be present in the blood and may be detected with a differential. Immature forms include metamyelocytes, myelocytes, promyelocytes, and/or blasts. Further work-up (e.g., bone marrow biopsy) may be necessary.
Long-term use of steroids or long-term exposure to toxic chemicals (such as lye or insecticides) can increase the risk of an abnormal differential.
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: ANA
• Allergies: Allergy tests
A "left shift" is a phrase used to note that there are a high number of 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.
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.
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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