Complete blood count (CBC)

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

Abnormal increases or decreases in cell counts as revealed in a complete blood count may indicate that you have an underlying medical condition that calls for further evaluation.

Why it's done How you prepare What you can expect Results

A complete blood count is a common blood test that's done for a variety of reasons:

  • To review your overall health. Your doctor may recommend a complete blood count as part of a routine medical examination to monitor your general health and to screen for a variety of disorders, such as anemia or leukemia.
  • To diagnose a medical condition. Your doctor may suggest a complete blood count if you're experiencing weakness, fatigue, fever, inflammation, bruising or bleeding. A complete blood count may help diagnose the cause of these signs and symptoms. If your doctor suspects you have an infection, the test can also help confirm that diagnosis.
  • To monitor a medical condition. If you've been diagnosed with a blood disorder that affects blood cell counts, your doctor may use complete blood counts to monitor your condition.
  • To monitor medical treatment. A complete blood count may be used to monitor your health if you're taking medications that may affect blood cell counts.
