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Definition
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.
Alternative Names
How the test is performed
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
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
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 Values
(cells/mcL = cells per microliter; gm/dL = grams per deciliter; pg/cell = picograms per cell)
What abnormal results mean
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.
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Reviewer Info: 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.; ADAM Health Illustrated Encyclopedia, 09/11/2006 |
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