CBC measures the number of three types of cells in your blood: Help diagnose other blood cancers, such as leukemia and lymphoma Find out if the cancer has spread to the bone marrow See how the human body reacts to cancer treatment Find other conditions, other than cancer If you receive chemotherapy, your doctor may check your blood cell count more often using CBC. What does a complete blood count measure? CBC measures the number of three types of cells in your blood: Number of white blood cells. The number of white blood cells, also called leukocytes, measures the total number of white blood cells in a blood sample. These cells protect the body from infection by attacking invading bacteria, viruses, and other foreign substances in the body. Some white blood cells can also attack cancer cells. Differences in white blood cells. The difference in white blood cells measures the amount of each type of white blood cell. There are five major types of white blood cells, and each type p...