Complete Blood Count (CBC)
Reviewed
Also called: CBC, Full blood count, FBC, Blood cell count
A complete blood count, or CBC, is a group of blood tests that measure the number and size of the different cells in your blood.
Specimen: Blood
Why this test may be ordered
- As part of a routine checkup or to monitor your overall health.
- To help diagnose blood diseases, infections, immune system disorders, or other medical conditions.
- To monitor a condition or treatment that may affect your blood cell counts, such as infections, anemia, immune system disorders, and blood cancers.
- To check for changes in an existing blood disorder.
Preparation and collection
Usually, no special preparation is necessary for a complete blood count. But if your provider ordered other tests on your blood sample, you may need to fast (not eat or drink) for several hours before the test.
A health care professional will take a blood sample from a vein in your arm, using a small needle. This usually takes less than five minutes.
There is very little risk to having a blood test. You may experience slight pain or bruising at the spot where the needle went in, but most symptoms go away quickly.
Understanding results
A CBC counts the cells in your blood. There are many reasons your levels may not be in the normal range.
- Abnormal red blood cells, hemoglobin, or hematocrit: Abnormal levels of red blood cells, hemoglobin, or hematocrit may be a sign of dehydration, anemia, heart disease, or too little iron in your body. Limitation: If any of your levels are abnormal, it doesn't always mean you have a medical condition that needs treatment. Next step: Talk with your provider to learn what your results mean. You may also need additional tests.
- Low white blood cell count: A low white cell count may be a sign of an autoimmune disorder, bone marrow disorder, or cancer. Limitation: A CBC test measures the total number of white cells in your blood. A different test called a CBC with differential measures the number of each type of these white blood cells. Next step: Your provider will consider your medical history, symptoms, and other factors to make a diagnosis. You may also need additional tests.
- High white blood cell count: A high white cell count may be a sign of an infection or a reaction to a medicine. Limitation: A complete blood count is only one tool your provider uses to learn about your health. Next step: Talk with your provider to learn what your results mean. Your provider will consider your medical history, symptoms, and other factors to make a diagnosis.
- If any of your levels are abnormal, it doesn't always mean you have a medical condition that needs treatment.
- Diet, activity level, medicines, having a menstrual period, not drinking enough water, and other factors can affect the results.
- A complete blood count is only one tool your provider uses to learn about your health. Your provider will consider your medical history, symptoms, and other factors to make a diagnosis.
What to do next
Talk with your provider to learn what your results mean. Your provider will consider your medical history, symptoms, and other factors to make a diagnosis. You may also need additional tests.
- What do my results mean for my health?
- Could my diet, activity, medicines, or not drinking enough water have affected my results?
- Do I need a CBC with differential or any other tests?
Evidence source
Source: U.S. National Library of Medicine (MedlinePlus). Practices and reference ranges may differ in your country.
U.S. National Library of Medicine: Complete Blood Count (CBC)