Blood tests can also give your doctor an idea of how well your organs are functioning and if they've been affected by cancer. Examples of blood tests used to diagnose cancer include: 1  Complete blood count (CBC). 2  This common blood test measures the amount of various types of blood cells in a sample of your blood.3  Blood cancers may be detected using this test if too many or too few of a type of blood cell or abnormal cells are found.xamples of blood tests used to diagnose cancer include: 1  Complete blood count (CBC). 2  This common blood test measures the amount of various types of blood cells in a sample of your blood.