Complete blood count (CBC)

A complete blood count (CBC) is a blood test. It's used to look at overall health and find a wide range of conditions, including anemia, infection and leukemia. A complete blood count test measures the following: Red blood cells, which carry oxygen White blood cells, which fight infection Hemoglobin, the oxygen-carrying protein in red blood cells Hematocrit, the amount of red blood cells in the blood Platelets, which help blood to clot

A complete blood count is a common blood test done for many reasons: To look at overall health. A complete blood count can be part of a medical exam to check general health and to look for conditions, such as anemia or leukemia. To diagnose a medical condition. A complete blood count can help find the cause of symptoms such as weakness, fatigue and fever. It also can help find the cause of swelling and pain, bruising, or bleeding. To check on a medical condition. A complete blood count can help keep an eye on conditions that affect blood cell counts. To check on medical treatment. A complete blood count may be used to keep an eye on treatment with medicines that affect blood cell counts and radiation.

If your blood sample is being tested only for a complete blood count, you can eat and drink as usual before the test. If your blood sample also will be used for other tests, you might need to fast for a certain amount of time before the test. Ask your health care provider what you need to do.

For a complete blood count, a member of the health care team takes a sample of blood by putting a needle into a vein in your arm, usually at the bend in your elbow. The blood sample is sent to a lab. After the test, you can return to your usual activities right away.