Patient education: Complete blood count (CBC) (The Basics)

What is a complete blood count? — A complete blood count is a test that gives information about the 3 main types of cells in the blood. This test is also called a "CBC" or "blood count." The cells the tests look at are:

●Red blood cells – These cells carry oxygen to your body.

●White blood cells – These cells fight infections. There are several types of white blood cells. Each type works in a different way.

●Platelets – Platelets help clots form so that you stop bleeding after you are injured.

A CBC measures the number of each of the 3 types of cells in your blood and shows if your levels are low, normal, or high. The test can also show if your body is making new blood cells.

The CBC has several ways to count red blood cells. These are called the hematocrit, hemoglobin, and red blood cell count. The CBC also measures the size and shape of the red blood cells. Some CBC tests also show if you are making new red blood cells, using a test called the "reticulocyte count."

Some CBC blood tests also include a "white blood cell differential." This tells you how many of each of the different types of white blood cells you have. It also shows if you have any abnormal white blood cells.

If the CBC shows something unexpected or something that requires a closer look at the cells, the lab can make something called a "blood smear." This lets them look at the cells under a microscope.

Why might a doctor or nurse order a CBC? — A CBC is done for many reasons. It might be done:

●To check for something called "anemia" if you are not feeling well or are feeling more tired than usual

●To check the infection-fighting cells, if you have signs of an infection

●To check the platelets, if you have signs of bleeding

●To make sure your blood counts are OK before surgery, especially a major operation

If you have had bleeding problems in the past, have certain diseases, or take certain medicines, a CBC might be done regularly to make sure your blood counts are OK.

If you are healthy and do not have any symptoms, a CBC is generally not needed as part of a routine check-up.

What can a CBC show? — The results of the test can show if you have different health conditions. Examples include:

●Too few red blood cells – This is called "anemia." Many things can cause anemia. They include not having enough iron, chronic (long-term) disorders like kidney disease, and certain blood disorders.

●Too many red blood cells – This is called "polycythemia" or "erythrocytosis." This can be caused by a blood disorder and is sometimes seen in people who smoke cigarettes.

●Too many white blood cells – This could be a sign of an infection or certain blood disorders.

●Too few platelets – This could be caused by an infection or certain blood disorders.

●Too many platelets – This could be caused by a blood disorder.

Certain medicines can also cause blood cell counts to be too low.