Complete Blood Count (CBC)
A comprehensive blood test that measures the components of your blood to evaluate overall health and detect a wide range of disorders.
{"Measures red blood cells, white blood cells, and platelets","Helps diagnose anemia, infection, and blood disorders","Includes hemoglobin, hematocrit, and differential counts","Typically requires a small blood sample","Often used as a routine health screening test"}
Key facts at a glance
- Category
- hematology
- Sample
- whole-blood
- Fasting
- false
What is a Complete Blood Count (CBC)?
A Complete Blood Count (CBC) is one of the most common blood tests performed in medical practice. It measures several components of your blood, including red blood cells (RBCs), white blood cells (WBCs), hemoglobin, hematocrit, and platelets. This test provides valuable information about your overall health and helps healthcare providers detect a variety of conditions, from anemia and infections to more serious blood disorders.
What does a CBC test measure?
A CBC test includes multiple measurements: Red Blood Cells (RBC) and related indices (hemoglobin, hematocrit, mean corpuscular volume) which carry oxygen throughout the body; White Blood Cells (WBC) which fight infection, including a differential count of different WBC types (neutrophils, lymphocytes, monocytes, eosinophils, basophils); and Platelets which help with blood clotting. Each of these components provides crucial information about your health status.
Why is a CBC performed?
A CBC may be ordered for several reasons: as a routine health checkup, to diagnose conditions like anemia, infection, or leukemia, to monitor existing conditions or treatment effects (especially during chemotherapy), to evaluate unexplained symptoms like fatigue, weakness, or fever, and to prepare for surgery as a baseline test. It is often one of the first tests ordered when a patient presents with nonspecific symptoms.
How is the test performed?
The CBC test is simple and quick. A healthcare professional will clean an area on your arm with antiseptic, insert a small needle into a vein, and collect a small sample of blood into a vial or test tube. The procedure usually takes less than five minutes. You may experience slight pain or bruising at the puncture site, but serious complications are rare. Fasting is typically not required for this test, though your doctor may advise otherwise based on your specific situation.
Understanding your results
CBC results are compared to reference ranges that vary based on age, sex, and sometimes ethnicity. Abnormal results do not always indicate a problem—slight variations can be normal for some individuals. Your healthcare provider will interpret your results in the context of your symptoms, medical history, and other test results. Follow-up testing may be recommended if any values fall outside the normal range.
Frequently asked questions
Do I need to fast before a CBC test?
How long does it take to get CBC results?
What can cause abnormal CBC results?
Is a CBC safe?
How often should I have a CBC?
Sources
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This information is for educational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment.
This content is for general informational and educational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment. Always seek the guidance of a qualified healthcare provider with any questions you have about a medical condition, and never disregard professional medical advice or delay seeking it because of something you read here.
If you think you may have a medical emergency, call your local emergency number or go to the nearest emergency department immediately.
Medically reviewed by WellAlly Editorial Team Last reviewed July 31, 2026. · Read our editorial policy