Is a CBC?
A complete blood count, or CBC, is an easy and very common
test that screens for certain disorders that can affect your health.
A CBC determines if there are any increases or decreases in
your cell counts. Normal values vary depending on your age and your gender.
Your lab report will tell you the normal value range for your age and gender.
A CBC can help diagnose a broad range of conditions, from anemia
and infection to cancer.
Three Basic Types of Blood Cells
Measuring changes in your blood cell levels can help your
doctor evaluate your overall health and detect disorders. The test measures the
three basic types of blood cells.
Red Blood Cells
Red blood cells carry oxygen throughout your body and remove
carbon dioxide. A CBC measures two components of your red blood cells:
- hemoglobin: oxygen-carrying protein
- hemocrit: percentage of red blood cells in your
Low levels of hemoglobin and hemocrit are often signs of
anemia, or blood that is deficient in iron.
White Blood Cells
White blood cells help your body fight infection. A CBC
measures the number and types of white blood cells in your body. Any abnormal
increases or decreases in the number or types of white blood cells could be a
sign of infection, inflammation, or cancer.
Platelets help your blood clot and control bleeding. When a
cut stops bleeding, it’s because platelets are doing their job. Any changes in platelet
levels can put you at risk for excessive bleeding and can be a sign of a
serious medical condition.
Is a CBC Ordered?
Your doctor may order a CBC as part of a routine checkup, or
if you have unexplained symptoms such as bleeding or bruising. A CBC can help
your doctor do the following.
Evaluate your overall health. Many doctors will order a CBC
so they can have a baseline view of your health. A CBC also helps your doctor
screen for any health problems.
Diagnose a health problem. Your doctor may order a CBC if
you have unexplained symptoms like weakness, tiredness, fever, redness,
swelling, bruising, or bleeding.
Monitor a health problem. Your doctor may order regular CBCs
to monitor your condition if you have been diagnosed with a disorder that
affects blood cell counts.
Monitor your treatment. Certain medical treatments can
affect your blood cell counts and may require regular CBCs. Your doctor can
evaluate how well your treatment is working based on your CBC.
Ready for a CBC
Make sure to wear a short-sleeved shirt, or a shirt with
sleeves that can be easily rolled up.
You can typically eat and drink normally before a CBC.
However, your doctor may require that you fast for a specific amount of time
before the test if the blood sample will be used for additional testing. Your
doctor will give you specific instructions.
Happens During a CBC?
During a CBC, a lab technician will draw blood from a vein,
typically from the inside of your elbow or from the back of your hand.
The technician will clean the surface of your skin with an
antiseptic and place an elastic band, or tourniquet, around your upper arm to
help the vein swell with blood. They’ll then insert a needle in the vein and
collect a blood sample in one or more vials. The technician will remove the
elastic band and cover the area with a bandage to stop the bleeding.
A blood test can be slightly uncomfortable. When the needle
punctures your skin, you might feel a prick or pinching sensation. Some people
also feel faint or light-headed when they see blood. You may experience minor
bruising, but this will clear up within a few days.
The test will take only a few minutes. Afterward, your
sample will be sent to a lab for analysis. Most results are available within a
few hours or a day after testing.
In young infants, the nurse will typically sterilize the
heel of the foot and use a small needle called a lancet to prick the area. The
nurse will then gently squeeze the heel and collect a small amount of blood in
a vial for testing.
Do the Results Mean?
Test results will vary based on your cell counts. Blood cell
counts that are too high or too low could signal a wide variety of conditions,
- iron or other vitamin and mineral deficiencies
- bleeding disorders
- heart disease
- autoimmune disorders
- bone marrow problems
- infection or inflammation
- reaction to medication
Your doctor will evaluate your results and diagnose your
condition. If your CBC shows abnormal levels, your doctor may order another
blood test to confirm results. They may also order other tests to help further
evaluate your condition and confirm a diagnosis.