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Complete Blood Count


What is it?

A complete blood count (CBC) is a commonly ordered blood test. A CBC is a group of tests that measures some of the different parts of the blood. Blood is made up of erythrocytes (a-RITH-ro-sites, red blood cells or RBCs), leukocytes (LEW-kuh-sites, white blood cells or WBCs), platelets, and plasma. The main part of the red blood cell is hemoglobin (HEEM-uh-glo-bun). Hemoglobin contains oxygen and iron. RBCs carry hemoglobin to deliver oxygen to your tissues. Hemoglobin also takes waste products such as carbon dioxide away from your tissues. WBCs help fight infections. There are different kinds of WBCs. The amounts of each kind of white blood cells help caregivers decide how to treat infections. Platelets, plasma, and other proteins in the blood help your blood clot when you are cut or hurt.

Why do I need it?

A CBC is usually done when you have a check-up. It is also done to check your health before surgery. A CBC can be helpful to find out why your skin is paler than usual. It can also help find out why you feel weak or tired. Other reasons for a CBC may be if you have fever, pain or swelling, or you bruise easily.

How do I get ready for the test?

You do not need to do anything special before having a CBC. The blood test may be done before or after eating and at any time of the day.

How is the blood collection done?

  • A caregiver will put a wide rubber strap around your arm and tighten it. Your skin will be cleaned with alcohol. A small needle attached to a special test tube will be put into a vein in your arm or hand. The tube has suction to pull the blood into it. When the tube is full, the rubber strap, needle and tube are removed. The caregiver will press a piece of cotton where the needle was removed. You may be asked to hold the cotton on the area for a few minutes to help stop the bleeding. Tape may then be put over the cotton on your arm.
  • Sometimes, for children, the blood may be taken from a small prick on the finger. The toe or heel of a baby may be used. You may be asked to hold the cotton on the area for a few minutes to help stop the bleeding.

What do I do after the test?

You may remove the tape and cotton from your arm in about 20 to 30 minutes. Call your caregiver to get the results of your test. The normal numbers for a CBC are different for men, women, and children. Your caregiver will explain what your test results mean for you. Follow the instructions of your caregiver.

Care Agreement

You have the right to help plan your care. To help with this plan, you must learn about your lab tests. You can then discuss the results with your caregivers. Work with them to decide what care may be used to treat you. You always have the right to refuse treatment. The above information is an educational aid only. It is not intended as medical advice for individual conditions or treatments. Talk to your doctor, nurse or pharmacist before following any medical regimen to see if it is safe and effective for you.

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