A complete blood count (CBC) is a blood test that gives important information about the kinds and numbers of cells in the blood, especially red blood cells, white blood cells, and platelets. A CBC helps your doctor evaluate symptoms (such as weakness, fatigue, or bruising) and diagnose conditions (such as anemia, infection, and many other disorders).

A CBC may be done to check for low red blood cells (anemia), problems with white blood cells, find an infection, find diseases of the blood, such as leukemia, or check to see if medicine or radiation treatment is working.