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
Blood counts may vary with altitude. In general, normal results are:
Male: 4.7 to 6.1 million cells/mcL
Female: 4.2 to 5.4 million cells/mcL
4,500 to 10,000 cells/mcL
Male: 40.7 to 50.3%
Female: 36.1 to 44.3%
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
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.
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:
Fainting or feeling light-headed
Hematoma (blood accumulating under the skin)
Infection (a slight risk any time the skin is broken)
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:
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.