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CBC

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Illustrations

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

Alternative Names    Return to top

Complete blood count

Definition    Return to top

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

CBC also includes information about the red blood cells that is calculated from the other measurements:

The platelet count is also usually included in the CBC.

How the Test is Performed    Return to top

Blood is drawn from a vein, usually from the inside of the elbow or the back of the hand. The puncture site is cleaned with antiseptic. An elastic band is placed around the upper arm to apply pressure and cause the vein to swell with blood.

A needle is inserted into the vein, and the blood is collected in an air-tight vial or a syringe. During the procedure, the band is removed to restore circulation. Once the blood has been collected, the needle is removed, and the puncture site is covered to stop any bleeding.

In infants or young children, the area is cleansed with antiseptic and punctured with a sharp needle or a lancet. The blood may be collected in a pipette (small glass tube), on a slide, onto a test strip, or into a small container. A bandage may be applied to the puncture site if there is any bleeding.

How to Prepare for the Test    Return to top

There is no special preparation needed.

How the Test Will Feel    Return to top

When the needle is inserted to draw blood, you may feel moderate pain, though most people feel only a prick or a stinging sensation. Afterward there may be some throbbing or bruising.

Why the Test is Performed    Return to top

The CBC is a screening test, used to diagnose and manage numerous diseases. The results can reflect problems with fluid volume (such as dehydration) or loss of blood. It can show abnormalities in the production, life span, and rate of destruction of blood cells. It can reflect acute or chronic infection, allergies, and problems with clotting.

MCV, MCH, and MCHC values reflect the size and hemoglobin concentration of individual cells, and are useful in the diagnosis of various types of anemia.

Normal Results    Return to top

(cells/mcL = cells per microliter; gm/dL = grams per deciliter; pg/cell = picograms per cell)

What Abnormal Results Mean    Return to top

High numbers of RBCs may indicate:

Low numbers of RBCs may indicate:

Low numbers of WBCs (leukopenia) may indicate:

High numbers of WBCs (leukocytosis) may indicate:

Low hematocrit may indicate:

High hematocrit may indicate:

Low hemoglobin values may indicate:

The test may be performed under many different conditions and in the assessment of many different diseases.

Risks    Return to top

Considerations    Return to top

Red blood cells transport hemoglobin which, in turn, transports oxygen. The amount of oxygen received by tissue depends on the amount and function of RBCs and hemoglobin. The MCV, MCH, and MCHC reflect the size and hemoglobin content of individual red blood cells.

The hematocrit is an expression of the proportion of whole blood that is composed of red blood cells (since the contribution by the WBCs is almost negligible). The hematocrit is a compound measure of RBC number and size.

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

Veins and arteries vary in size from one patient to another and from one side of the body to the other. Obtaining a blood sample from some people may be more difficult than from others.

Update Date: 9/11/2006

Updated by: Corey Cutler, MD, MPH, FRCP(C), Assistant Professor of Medicine, Harvard Medical School; Department of Medical Oncology, Dana-Farber Cancer Institute, Boston, MA. Review provided by VeriMed Healthcare Network.

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