Complete Blood Count (CBC)

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. A CBC measures: Red blood cells, which carry oxygen from your lungs to the rest of your body.; White blood cells, which fight infections and other diseases. There are five major types of white blood cells.

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.; Platelets, which stop bleeding by helping your blood to clot.; Hemoglobin, an iron-rich protein in red blood cells that carries oxygen from your lungs to the rest of your body.; Hematocrit, the amount of whole blood that is made up of red blood cells.; Mean corpuscular volume (MCV), the average size of your red blood cells.; Other names for a complete blood count: CBC, full blood count, blood cell count

Why this test is done

Your health care provider may have ordered a complete blood count as part of your checkup or to monitor your overall health. The test may also be used to:

• Help diagnose blood diseases, infections, immune system disorders, or other medical conditions
• Check for changes in an existing blood disorder

How to prepare

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. Your provider will let you know if there are any special instructions.

Sample type

Blood