Complete Blood Count

A Complete Blood Count (CBC) test is the most commonly ordered blood test and is used to:

  • Evaluate overall health
  • Screen for a variety of disorders e.g. anemia, infection etc.
  • Check the bone marrow and spleen functioning
  • Monitor an existing condition e.g. blood disorders.
  • Monitor treatment such as chemotherapy or radiation therapy

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.

When should I get a complete blood count?

The CBC is a very common test. You may have a CBC performed when you have a routine health examination, when you are being diagnosed or assessed for a disease or condition, or when your provider is monitoring the effectiveness of a treatment. Because blood counts can be affected by a diverse range of health conditions, the CBC may be recommended by your doctor to help identify the cause of many different kinds of symptoms. Your health care provider is in the best position to address whether a CBC is appropriate in your specific situation.

How you prepare?

If your blood sample is being tested only for a complete blood count, you can eat and drink normally before the test. If your blood sample will be used for additional tests, you may need to fast for a certain amount of time before the test. Your doctor will give you specific instructions you need to contact your doctor.

What you can expect

For a complete blood count, a member of your health care team takes a sample of blood by inserting a needle into a vein in your arm, usually at the bend in your elbow. The blood sample is sent to a lab for analysis. You can return to your usual activities immediately.