Why do I need a Complete Blood Count (CBC)?A CBC is the most frequently performed lab test. It provides a great deal of information about the three kinds of cells in the blood - red blood cells, white blood cells, and platelets. It is most frequently used as a screening test, as an anemia check, and as a test for infection, but it is also used to aid in the diagnosis and treatment of a large number of other conditions. Included in the CBC are hematocrit, hemoglobin, red blood cell count, red blood cell indices, white blood cell count, white blood cell differential, and platelet count. CBC blood test can give you information about anemia (a decrease in the ability of the red blood cells to transport oxygen to the tissues of the body) and infections, as well as blood disorders such as leukemia. In addition to red blood cells, the CBC blood test measures the amount of white blood cells. Elevated white blood cells on a CBC blood test may mean that you currently have an infection. If your CBC shows low levels, you might have a difficult time fighting off an infection.Platelets, also made in the bone barrow, are checked on a CBC blood test. Platelets create clots to help stop bleeding from an injury. If your CBC blood test reveals low platelet levels, you might be more susceptible to bleeding. High platelet levels could mean that you have an increased risk of internal clots.Hemoglobin is measured in a CBC blood test. Red blood cells use hemoglobin to bring oxygen to the rest of the body and to bring carbon dioxide back to the lungs. Low hemoglobin levels shown on a CBC blood test can also be a sign of anemia. Hematocrit is measured in a CBC blood test and measures the proportion of blood that is filled with red blood cells. Low hematocrit can indicate anemia or leukemia. High hematocrit levels on a CBC blood test may indicate dehydration or excessive red blood cells.