| Definition: |
A blood test that measures the number of red blood cells (RBCs). The RBC count is almost always ordered as part of the complete blood count (CBC) test.
RBCs transport hemoglobin which, in turn, transports oxygen. The amount of oxygen received by tissue is dependent on the amount and function of RBCs and hemoglobin. RBCs normally survive for about 120 days in the blood; they are then removed by phagocytic cells in the spleen or Kupffer cells in the liver.
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| Alternative Names: |
Erythrocyte count; Red blood cell count
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| How the test is performed: |
Adult or child:
Blood is drawn from a vein (venipuncture), usually from the inside of the elbow or the back of the hand. The puncture site is cleaned with antiseptic, and a tourniquet (an elastic band) or blood pressure cuff is placed around the upper arm to apply pressure and restrict blood flow through the vein. This causes veins below the tourniquet to distend (fill 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 tourniquet 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.
Infant or young child:
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. Cotton or a bandage may be applied to the puncture site if there is any continued bleeding. |
| How to prepare for the test: |
Adults:
No special preparation is necessary.
Infants and children:
The physical and psychological preparation you can provide for this or any test or procedure depends on your child's age, interests, previous experiences, and level of trust. For specific information regarding how you can prepare your child, see the following topics as they correspond to your child's age:
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| How the test will feel: |
| When the needle is inserted to draw blood, some people feel moderate pain, while others feel only a prick or stinging sensation. Afterward, there may be some throbbing. |
| Why the test is performed: |
| This test can help in assessment of anemia (low hemoglobin) as well as other conditions affecting the red blood cell compartment. |
| Normal Values: |
RBC (varies with altitude):
- male: 4.7 to 6.1 million cells/mcl
- female: 4.2 to 5.4 million cells/mcl
Note: cells/mcl = cells per microliter |
| What abnormal results mean: |
Abnormal RBCs have a shorter life span. Intravascular RBC trauma, such as that caused by artificial heart valves or peripheral vascular (blood vessel) atherosclerotic plaques can damage RBCs. An enlarged spleen such as that caused by portal hypertension or leukemia may remove normal red cells as well as senescent (aging) ones. High numbers of RBCs may indicate:
Low oxygen tension in the blood from:
Low numbers of RBCs may indicate:
nutritional deficiencies of:
Additional conditions under which the test may be performed:
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| What the risks are: |
- excessive bleeding
- fainting or feeling light-headed
- hematoma (blood accumulating under the skin)
- infection (a slight risk any time the skin is broken)
- multiple punctures to locate veins
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| Special considerations: |
The RBC count may be decreased during pregnancy because of an increase in body fluids.
The RBC will increase over a period of several weeks after moving to a higher altitude.
Dehydration increases the RBC count.
Drugs that can increase the RBC count include gentamicin and methyldopa. Drugs that can decrease the RBC count include chloramphenicol, hydantoins, and quinidine.
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. |
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