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A.D.A.M. Medical Encyclopedia [Internet]. Atlanta (GA): A.D.A.M.; 2013.

A.D.A.M. Medical Encyclopedia.

CBC

Complete blood count

Last reviewed: March 19, 2012.

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

The CBC test also provides information about the following measurements:

  • Average red blood cell size (MCV)
  • Hemoglobin amount per red blood cell (MCH)
  • The amount of hemoglobin relative to the size of the cell (hemoglobin concentration) per red blood cell (MCHC)

The platelet count is also usually included in the CBC. 

How the Test is Performed

A blood sample is needed. For information on how this is done, see: Venipuncture

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, though most people feel only a prick or a stinging sensation. Afterward there may be some throbbing or bruising.

Why the Test is Performed

A complete blood count (CBC) is used to detect or monitor many different health conditions. It may be used to:

  • Diagnose infections or allergies
  • Detect blood clotting problems or blood disorders, including anemia
  • Evaluate red blood cell production or destruction

Normal Results

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

RBC count:

  • Male: 4.7 to 6.1 million cells/mcL
  • Female: 4.2 to 5.4 million cells/mcL

WBC count:

  • 4,500 to 10,000 cells/mcL

Hematocrit:

  • Male: 40.7 to 50.3%
  • Female: 36.1 to 44.3%

Hemoglobin:

  • Male: 13.8 to 17.2 gm/dL
  • Female: 12.1 to 15.1 gm/dL

Red blood cell indices:

  • MCV: 80 to 95 femtoliter
  • MCH: 27 to 31 pg/cell
  • MCHC: 32 to 36 gm/dL

Note:

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

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

A high RBC or hematocrit may be due to:

A low RBC 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:

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

Low hemoglobin values may be due to:

Risks

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:

  • Excessive bleeding
  • Fainting or feeling light-headed
  • Hematoma (blood accumulating under the skin)
  • Infection (a slight risk any time the skin is broken)

Considerations

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:

References

  1. Goldman L, Schafer AI, eds. Cecil Medicine. 24th ed. Philadelphia, Pa: Saunders Elsevier; 2011:chap 161.

Review Date: 3/19/2012.

Reviewed 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. Health Solutions, Ebix, Inc.

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