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CBC blood test

Complete blood count

A complete blood count (CBC) test measures the following:

The CBC test also provides information about the following measurements:

The platelet count is also usually included in the CBC.


Red blood cells, sickle cell
Megaloblastic anemia - view of red blood cells
Red blood cells, tear-drop shape
Red blood cells, normal
Red blood cells, elliptocytosis
Red blood cells, spherocytosis
Red blood cells, multiple sickle cells
Basophil (close-up)
Malaria, microscopic view of cellular parasites
Malaria, photomicrograph of cellular parasites
Red blood cells, sickle cells
Red blood cells, sickle and pappenheimer
Red blood cells, target cells
Formed elements of blood


Complete blood count - series

I Would Like to Learn About:

How the Test is Performed

A blood sample is needed.

How to Prepare for the Test

There is no special preparation needed.

How the Test will Feel

When the needle is inserted to draw blood, you may feel moderate pain. Some people feel only a prick or stinging. Afterward there may be some throbbing or slight bruising. This soon goes away.

Why the Test is Performed

A complete blood count (CBC) is a commonly performed lab test. It can be used to detect or monitor many different health conditions. Your health care provider may order this test:

Normal Results

Blood counts may vary with altitude. In general, normal results are:

RBC count:

WBC count:



Red blood cell indices:

Platelet count:

The examples above are common measurements for results of these tests. Normal value ranges may vary slightly among different laboratories. Some labs use different measurements or test different samples. Talk to your doctor about the meaning of your specific test results.

What Abnormal Results Mean

High RBC, hemoglobin, or hematocrit may be due to:

Low RBC, hemoglobin, or hematacrit is a sign of anemia, which can result from:

A lower than normal white blood cell count is called leukopenia. A decreased WBC count may be due to:

A high WBC count is called leukocytosis. It can result from:

A high platelet count may be due to:

A low platelet count may be due to:


There is very little risk involved with having your blood taken. Veins and arteries vary in size from one person to another and from one side of the body to the other. Taking blood from some people may be more difficult than from others.

Other risks associated with having blood drawn are slight but may include:


RBCs transport hemoglobin which, in turn, carries oxygen. The amount of oxygen received by body tissues depends on the amount and function of RBCs and hemoglobin.

WBCs are mediators of inflammation and the immune response. There are various types of WBCs that normally appear in the blood:

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Vajpayee N, Graham SS, Bem S. Basic examination of blood and bone marrow. In: McPherson RA, Pincus MR, eds. Henry's Clinical Diagnosis and Management by Laboratory Methods. 22nd ed. Philadelphia, PA: Elsevier Saunders; 2011:chap 30.


Review Date: 11/26/2014  

Reviewed By: Yi-Bin Chen, MD, Leukemia/Bone Marrow Transplant Program, Massachusetts General Hospital, Boston, MA. Also reviewed by David Zieve, MD, MHA, Isla Ogilvie, PhD, and the A.D.A.M. Editorial team.

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