White Blood Cell Count and Differential
A white blood cell (WBC) count measures the number of white blood cells
in your blood. A WBC differential determines the percentage of each type of
white blood cell present in your blood. A differential can also detect immature
white blood cells or any abnormalities, both of which are signs of a potential
A WBC count may also be called a leukocyte count, and a WBC
differential count may be called a leukocyte differential count.
What Does a White Blood Cell Count and Differential Address?
White blood cells are an important part of your body’s immune system: They
are responsible for protecting your body against infections and invading
organisms. You have five types of white blood cells: neutrophils, lymphocytes,
monocytes, eosinophils, and basophils. Each of these is affected in a different
way depending on the condition or disease that is affecting your WBC counts.
Your doctor may request a WBC count and differentials if he or she suspects
you have one of several conditions, including:
Both the WBC count and WBC differential can provide your doctor with
clues as to why you have elevated or low white blood cell numbers. Both tests
can also help your doctor know if your condition is getting worse or improving.
WBC counts that return to normal indicate a condition is improving. WBC counts
that do not change or worsen indicate a condition that is not being treated
How Is a White Blood Cell Count and Differential Administered?
To conduct a WBC count and differential, your doctor will need to
collect a blood sample from you. Blood is typically drawn from a vein in either
the bend of your arm or on your hand. (In children and infants, blood can be
taken from a heel or finger stick.) Your healthcare provider may use a
tourniquet to restrict blood flow and help the veins in your arm provide a sufficient
Once the blood is collected, it is sent to a lab for analysis.
What Are the Risks of a White Blood Cell Count and Differential?
WBC count and differential tests have very few potential risks. Apart
from bruising or soreness at the puncture site, this test should not cause any
problems or complications. Some people may feel moderate pain and a stinging
sensation during the blood draw. Some people may feel sick or lightheaded
during or after the blood draw. If you do, let your healthcare provider know,
and remain seated until the feeling has passed.
Rarely, people who have had blood drawn develop a hematoma, an
accumulation of blood directly under the skin. People who have blood collected
may also develop an infection as a result of the collection, but this is also
No special preparation is necessary for a WBC count or differential.
Your doctor may ask you to stop taking certain medications, including
over-the-counter supplements or vitamins, for several days before the sample
collection occurs. Medicines, both prescription and over-the-counter, can
affect white blood cell counts.
What Can a Patient Expect Afterward?
Once your healthcare provider has enough blood to conduct a WBC count
and differential, he or she will remove the needle and place moderate pressure
on the injection site to stop any bleeding. The blood is shipped directly to a
lab for analysis. Depending on which tests your doctor ordered, you may wait
several days for results.
A single WBC count or differential test does not tell the whole story
of what’s going on with your body. However, both tests are important tools for
doctors looking to find out what might be causing your symptoms. These differential
results may indicate certain conditions, as is discussed below.
An increase in neutrophils in your blood may be caused by:
- acute stress
- an infection
- rheumatoid arthritis
A decrease in neutrophils in your blood may be caused by:
- bacterial infection
- radiation exposure
An increase in lymphocytes in your blood may be caused by:
- chronic infection
- an infectious viral infection, such as the mumps
A decrease in lymphocytes may be caused by:
- HIV infection
- radiation exposure (from radiation therapy or accidental)
An increase in monocytes may be caused by:
- chronic inflammatory disease
- viral infection, such as measles, mononucelosis,
An increase in eosinophils may be caused by:
- an allergic reaction
- parasitic infection
A decrease in basophils may be caused by acute allergic reaction.