A complete blood count (CBC) is a common medical test that measures the main components of the patients blood, including the number of red blood cells, white blood cells, and platelets. While a CBC test may be used to diagnose some blood cancers, such as leukemia, it is not typically used to diagnose solid tumor cancers. However, a CBC test can be used to help diagnose some blood cancers, such as leukemia and lymphoma, and to monitor how cancer or its treatment is affecting the body. In addition, a CBC test can help doctors diagnose and monitor noncancerous conditions during cancer treatment. Therefore, a CBC test can provide clues to possible health problems and help doctors decide whether other tests or procedures are needed to make a diagnosis. However, routine bloodwork, including a CBC test, will not detect most cancers. Other blood tests, such as blood chemistry and tumor marker tests, can also provide clues that bear investigation and inform treatment decisions.