Test Overview A complete blood count CBC gives important information about the kinds and numbers of cells in the blood, especially red blood cells , white blood cells , and platelets. White blood cells protect the body against infection. If an infection develops, white blood cells attack and destroy the bacteria, virus, or other organism causing it. White blood cells are bigger than red blood cells but fewer in number.
When a person has a bacterial infection, the number of white cells rises very quickly. The number of white blood cells is sometimes used to find an infection or to see how the body is dealing with cancer treatment. White blood cell types WBC differential. The major types of white blood cells are neutrophils , lymphocytes, monocytes, eosinophils, and basophils.
Immature neutrophils, called band neutrophils, are also part of this test. Each type of cell plays a different role in protecting the body. The numbers of each one of these types of white blood cells give important information about the immune system. Too many or too few of the different types of white blood cells can help find an infection, an allergic or toxic reaction to medicines or chemicals, and many conditions, such as leukemia. Red blood cell RBC count.
Red blood cells carry oxygen from the lungs to the rest of the body. They also carry carbon dioxide back to the lungs so it can be exhaled. If the RBC count is low anemia , the body may not be getting the oxygen it needs. If the count is too high a condition called polycythemia , there is a chance that the red blood cells will clump together and block tiny blood vessels capillaries.
This also makes it hard for your red blood cells to carry oxygen. This test measures the amount of space volume red blood cells take up in the blood. The value is given as a percentage of red blood cells in a volume of blood. Hematocrit and hemoglobin values are the two major tests that show if anemia or polycythemia is present. Hemoglobin Hgb. The hemoglobin molecule fills up the red blood cells. It carries oxygen and gives the blood cell its red colour. The hemoglobin test measures the amount of hemoglobin in blood and is a good measure of the blood's ability to carry oxygen throughout the body.
Red blood cell indices. They are measured by a machine and their values come from other measurements in a CBC. The MCV shows the size of the red blood cells. The MCH value is the amount of hemoglobin in an average red blood cell. The MCHC measures the concentration of hemoglobin in an average red blood cell. These numbers help in the diagnosis of different types of anemia.
Red cell distribution width RDW can also be measured which shows if the cells are all the same or different sizes or shapes.
Platelet thrombocyte count. Platelets thrombocytes are the smallest type of blood cell. They are important in blood clotting. When bleeding occurs, the platelets swell, clump together, and form a sticky plug that helps stop the bleeding. If there are too few platelets, uncontrolled bleeding may be a problem.
If there are too many platelets, there is a chance of a blood clot forming in a blood vessel. Also, platelets may be involved in hardening of the arteries atherosclerosis. Mean platelet volume MPV. Mean platelet volume measures the average amount volume of platelets.
Mean platelet volume is used along with platelet count to diagnose some diseases. If the platelet count is normal, the mean platelet volume can still be too high or too low. Why It Is Done A complete blood count may be done to: Find the cause of symptoms such as fatigue, weakness, fever, bruising, or weight loss.
Check for anemia. See how much blood has been lost if there is bleeding. Diagnose polycythemia. A red blood cell count that's higher than normal erythrocytosis , or high hemoglobin or hematocrit levels, could point to an underlying medical condition, such as polycythemia vera or heart disease.
White blood cell count. A low white blood cell count leukopenia may be caused by a medical condition, such as an autoimmune disorder that destroys white blood cells, bone marrow problems or cancer.
Certain medications also can cause white blood cell counts to drop. If your white blood cell count is higher than normal, you may have an infection or inflammation. Or, it could indicate that you have an immune system disorder or a bone marrow disease. A high white blood cell count can also be a reaction to medication. For specifics about what your complete blood count results mean if they fall outside the normal ranges, talk to your doctor.
Mayo Clinic does not endorse companies or products. Advertising revenue supports our not-for-profit mission. This content does not have an English version. This content does not have an Arabic version. Overview A complete blood count CBC is a blood test used to evaluate your overall health and detect a wide range of disorders, including anemia, infection and leukemia. A complete blood count test measures several components and features of your blood, including: Red blood cells, which carry oxygen White blood cells, which fight infection Hemoglobin, the oxygen-carrying protein in red blood cells Hematocrit, the proportion of red blood cells to the fluid component, or plasma, in your blood Platelets, which help with blood clotting.
Request an Appointment at Mayo Clinic. Collecting a sample of blood is only temporarily uncomfortable and can feel like a quick pinprick. Parents usually can stay with their child during a blood test. Encourage your child to relax and stay still because tensing muscles can make it harder to draw blood. Your child might want to look away when the needle is inserted and the blood is collected.
Help your child to relax by taking slow deep breaths or singing a favorite song. Most blood tests take just a few minutes. Occasionally, it can be hard to find a vein so the health professional may need to try more than once. The health professional will remove the elastic band and the needle and cover the area with cotton or a bandage to stop the bleeding.
Afterward, there may be some mild bruising, which should go away in a few days. Blood samples are processed by a machine, and it may take a few hours to a day for the results to be available. If the test results show signs of a problem, the doctor might order other tests to figure out what the problem is and how to treat it.
A CBC is a safe procedure with minimal risks. Some kids might feel faint or lightheaded from the test.
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