What Is a Complete Blood Count and Why Is It Done? Doctors may
want you to get a type of medical test called a complete blood
count (CBC) if you're feeling more tired than usual, seem to
have an infection, or have unexplained bruising or bleeding. The
CBC is a common blood test that helps doctors get information
about the three major types of cells in the blood: - Red blood
cells. These are the cells that carry oxygen from the lungs to
the rest of the body. The CBC measures the number of red blood
cells in the body, along with other information about red blood
cells, such as amounts of an oxygen-carrying protein called
hemoglobin. This information can help doctors test a person for
anemia, which can happen due to loss of blood, or problems with
the production or destruction of red blood cells. - White blood
cells. These cells help the body fight infection. The CBC
measures the number of white blood cells (also called
leukocytes) in the blood and also looks at the different types
of white blood cells in the bl