A complete blood count (CBC) is a blood test. It gives your provider information about your blood and overall health. CBCs help providers diagnose, monitor and screen for a wide range of diseases, conditions, disorders and infections. Your provider takes a sample of blood and your lab results are usually ready within a few days.
A complete blood count (CBC) is a blood test. It helps healthcare providers detect a range of disorders and conditions. It also checks your blood for signs of medication side effects. Providers use this test to screen for diseases and adjust treatments.
A CBC measures and counts your blood cells. Your provider takes a sample of your blood and sends it to a lab. The lab does a series of tests to evaluate your blood cells. These tests help your provider monitor your health.
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You may need a CBC if you have symptoms such as:
CBCs are an important part of a yearly physical exam. Providers also order CBCs to monitor the side effects of some prescription medications.
Your provider may order a CBC to:
A CBC does many tests to measure and study red blood cells, white blood cells and platelets. Red blood cells carry oxygen throughout the body. White blood cells are part of your immune system. They help your body fight infection. Platelets help your body clot.
A CBC measures, counts, evaluates and studies many aspects of your blood:
A CBC tells your provider:
A CBC blood test can help your provider diagnose a wide range of conditions, disorders, diseases and infections, including:
You don’t need to do anything to prepare for a CBC. Your provider cleans your arm and inserts a needle. The needle may sting or pinch a little, but it shouldn’t hurt. In infants, providers usually insert the needle into the baby’s heel.
Through the needle, your provider removes a sample of your blood and collects it in a tube. Sometimes, your provider takes more than one tube of blood.
After drawing blood, your provider removes the needle and places a bandage on your arm. Your provider sends the blood to a lab. Your body quickly rebuilds its blood supply.
You’ll have some gauze and a bandage on your arm, secured with tape. Your arm may be a little sore for a few hours. You may develop a small bruise where your provider inserted the needle.
A CBC gives your provider a picture of your overall health. Using a small amount of blood, a CBC can help detect hundreds of conditions, disorders and infections. It allows your provider to monitor your health, screen for disease and plan and adjust treatment.
A CBC is a safe, common test. There are no risks involved, and your provider only removes a small amount of blood. Rarely, some people feel a little faint or lightheaded after a CBC.
Results are usually ready within a few days. Sometimes it only takes 24 hours to get results. Your provider will contact you to explain the results and discuss next steps. If your blood cell counts are outside of the normal range, your provider may order follow-up tests.
What are the normal ranges for a complete blood count?
Hemoglobin normal range:
Hematocrit normal range:
Platelet Count normal range:
White blood cell (WBC) normal range:
Your provider will review the results of your CBC with you. If you have questions about the results, call your provider.
A note from Cleveland Clinic
Healthcare providers use complete blood counts to manage disease and help you stay healthy. With one sample of blood, CBCs can help screen for hundreds of disorders, conditions and infections. A CBC can detect conditions early, sometimes before you have symptoms, so treatment can start as soon as possible. CBCs are an essential tool in maintaining good overall health.
Last reviewed by a Cleveland Clinic medical professional on 03/02/2021.
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