The complete blood count (CBC) is a common blood test that evaluates the three major types of cells in the blood: red blood cells, white blood cells, and platelets.
A CBC may be ordered as part of a routine checkup, or if your child is feeling more tired than usual, seems to have an infection, or has unexplained bruising or bleeding.
The CBC can also test for loss of blood, abnormalities in the production or destruction of blood cells, acute and chronic infections, allergies, and problems with blood clotting.
No special preparations are needed. Having your child wear a T-shirt or short-sleeved shirt on the day of the test can make things easier for the technician who will be drawing blood.
Not much blood is drawn in a CBC. A health professional will usually draw the blood from a vein. For an infant, the blood may be obtained by puncturing the heel with a small needle (lancet). If the blood is being drawn from a vein, the skin surface is cleaned with antiseptic, and an elastic band (tourniquet) is placed around the upper arm to apply pressure and cause the veins to swell with blood. A needle is inserted into a vein (usually in the arm inside of the elbow or on the back of the hand) and blood is withdrawn and collected in a vial or syringe.
After the procedure, the elastic band is removed. Once the blood has been collected, the needle is removed and the area is covered with cotton or a bandage to stop the bleeding. Collecting blood for this test will only take a few minutes.
Either method (heel sticking or vein withdrawal) of collecting a sample of blood is only temporarily uncomfortable and can feel like a quick pinprick. Afterward, there may be some mild bruising, which should go away in a few days.
The blood sample is processed by a machine. Parts of the CBC results can be available in minutes in an emergency, but more commonly the full test results come after a few hours or the next day.
If a CBC test points to anemia, infection, or other concerns, your child's doctor may repeat the test just to be sure. If the second set of test results come back the same, your doctor will likely order further lab tests for your child to determine what's causing the problem and how to treat it.
The CBC test is considered a safe procedure. However, as with many medical tests, there are some problems that can occur with having blood drawn, such as:
Having a blood test is relatively painless. Still, many kids are afraid of needles. Explaining the test in terms your child can understand might help ease some of the fear.
Allow your child to ask the technician any questions he or she might have. Tell your child to try to relax and stay still during the procedure, as tensing muscles and moving can make it harder and more painful to draw blood. It also may help if your child looks away when the needle is being inserted into the skin.
If you have questions about the CBC test, contact your doctor. You also can talk to the technician before the procedure.
Reviewed by: Yamini Durani, MD
Date reviewed: August 2014
|National Heart, Lung, and Blood Institute (NHLBI) The NHLBI provides the public with educational resources relating to the treatment of heart, blood vessel, lung, and blood diseases as well as sleep disorders.|
|American Medical Association (AMA) The AMA has made a commitment to medicine by making doctors more accessible to their patients. Contact the AMA at: American Medical Association|
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|Centers for Disease Control and Prevention (CDC) The CDC (the national public health institute of the United States) promotes health and quality of life by preventing and controlling disease, injury, and disability.|
|American Society of Hematology This group provides information relating to blood, blood-forming tissues, and blood diseases.|
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