About the Test
Purpose of the test
The WBC differential is often used as part of a 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 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)
What does the test measure?
A WBC differential measures the number and/or the percentage of each type of WBC present in your sample of blood at the time of the test. Also called leukocytes, WBCs 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 a sample of your blood. There are five main types of WBCs, each with different functions. The differential shows if:
- The different types of WBCs are present in normal proportion to one another
- The numbers of the different cell types are normal, increased, or decreased
- Abnormal and/or immature WBCs are present
This information is helpful in diagnosing specific types of illnesses that affect the immune system and the bone marrow.
When should I get a WBC differential test?
You may have a 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 health care 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.
Finding a WBC Differential Test
How can I get a WBC Differential test?
A WBC differential is typically performed in conjunction with a CBC to evaluate the different types of blood cells. It may be used to help diagnose and/or monitor numerous conditions that affect WBC populations. You can also order a CBC test online (which includes WBC differential) with testing by a Clinical Laboratory Improvement Amendments (CLIA)-approved lab.
A WBC differential may also be ordered on a regular basis if you are being treated or monitored for a WBC-related disease.
Can I take the test at home?
Due to the nature of the test and sample collection, a WBC differential cannot be done at home and must be administered by a health professional. However, the test can be ordered online and then performed at a local testing location at your convenience.
How much does the test cost?
Several factors can affect the cost of a WBC differential, including technician fees for obtaining a blood sample, fees for analysis, and charges for office visits. These costs are often covered by health insurance if the test is prescribed by your doctor.
Check with your doctor and insurance provider to find out about copays, deductibles, and any other charges if you get a WBC differential.
Taking a WBC Differential Test
WBC differentials require a blood sample to be taken, typically drawn from a vein in your arm or by pricking a finger. The test is administered in a clinical setting by a health care professional.
Before the test
There is no preparation required prior to a WBC differential. If your doctor has ordered other blood tests to be run in conjunction with the test, you may be required to fast for several hours prior to the test, though.
During the test
A medical professional will take a blood sample from a vein in your arm using a needle. You will have an elastic band tied around your upper arm, and the inside of your elbow will be cleaned with an antiseptic pad. A needle will be inserted into the vein, a vial of blood will be drawn, and then the needle will be removed. The entire process usually lasts less than a few minutes during which there may be some temporary pain as the needle is inserted and withdrawn.
After the test
After blood is drawn with a needle, a bandage is applied, and you may need to apply light pressure for a few minutes to help prevent bleeding. There may be tenderness at the puncture site, and some light bruising may occur. You can usually return to normal activities once the test is complete.
WBC Differential Test Results
Receiving test results
The results of your test are usually ready within a few days. You may receive your results through an online health portal or in the mail. Your doctor may contact you to talk with you about your test results and to discuss if any follow-up is needed.
Interpreting test results
WBC differential results indicate the number and/or the percentage of each type of WBC that is present in your sample of blood at the time of the test.
Results of a differential are usually reported as absolute values 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.
When interpreting the results of your differential, your health care 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.
Many factors can cause a temporary rise or drop in the number of any type of WBC. A persistent increase or decrease will usually prompt your health care practitioner to order more testing to determine the cause. If your result is barely outside the reference range it may or may not be significant, while a large rise or drop in one or more types of WBCs usually prompts more or repeat testing.
If results indicate a problem, a wide variety of other tests may be performed to help determine the cause. A health care 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.
After you receive your results, you may want to ask your doctor one of the following questions:
- My CBC report includes a result for immature granulocytes (IG). What are they?
- If I have an abnormal result on my WBC differential, what other tests might I need?
- My report mentions a “left shift.” What does this mean?
