Medical Encyclopedia

 

Medical Encyclopedia

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CBC

Contents of this page:

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:

The CBC test also provides specific information the size and hemoglobin content of individual red blood cells. This is determined from the additional following measurements:

The platelet count is also usually included in the CBC.

See also:

How the Test is Performed    Return to top

Blood is typically drawn from a vein, usually from the inside of the elbow or the back of the hand. The site is cleaned with germ-killing medicine (antiseptic). The health care provider wraps an elastic band around the upper arm to apply pressure to the area and make the vein swell with blood.

Next, the health care provider gently inserts a needle into the vein. The blood collects into an airtight vial or tube attached to the needle. The elastic band is removed from your arm.

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, a sharp tool called a lancet may be used to puncture the skin and make it bleed. The blood collects into a small glass tube called a pipette, or onto a slide or test strip. A bandage may be placed over the area 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 test may be performed under many different conditions and in the assessment of many different diseases. It 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. The test can reveal problems with red blood cell production and destruction, or help diagnose infection, allergies, and problems with blood clotting.

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

Normal Results    Return to top

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

Note: Normal value ranges may vary slightly among different laboratories. Talk to your doctor about the meaning of your specific test results.

What Abnormal Results Mean    Return to top

High numbers of RBCs or a high hematocrit may be due to:

Low numbers of RBCs or low hematocrit indicates anemia, which can result from:

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

High numbers of WBCs is called leukocytosis. It can result from:

Low hemoglobin values may indicate:

Risks    Return to top

There is very little risk involved with having your blood taken. Veins and arteries vary in size from one patient 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:

Considerations    Return to top

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:

Update Date: 8/10/2008

Updated by: David C. Dugdale, III, MD, Professor of Medicine, Division of General Medicine, Department of Medicine, University of Washington School of Medicine. Also reviewed by David Zieve, MD, MHA, Medical Director, A.D.A.M., Inc.

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The information provided herein should not be used during any medical emergency or for the diagnosis or treatment of any medical condition. A licensed physician should be consulted for diagnosis and treatment of any and all medical conditions. Call 911 for all medical emergencies. Links to other sites are provided for information only -- they do not constitute endorsements of those other sites. Copyright 1997-2009, A.D.A.M., Inc. Any duplication or distribution of the information contained herein is strictly prohibited.