Red Blood Cell Count

Red Blood Cell Count

Does this test have other names?

RBC count, erythrocyte count

What is this test?

This test measures the number of red blood cells, or erythrocytes, in your blood. Red blood cells play a critical role in moving oxygen from your lungs to the rest of your body and returning carbon dioxide to your lungs to be exhaled.

A red blood cell count is typically done as part of a complete blood count (CBC), which is a screening test to check for a variety of medical conditions.

Why do I need this test?

You may have this blood test as part of a general checkup. You may also have this test to look for specific health problems, such as internal bleeding, anemia, and certain cancers.

What other tests might I have along with this test?

A red blood cell count is often part of a complete blood count, so other components of your blood, such as white blood cells and platelets, are also measured.

If your health care provider suspects you have a particular illness, he or she may also order other tests necessary for making a diagnosis.

What do my test results mean?

Many things may affect your lab test results. These include the method each lab uses to do the test. Even if your test results are different from the normal value, you may not have a problem. To learn what the results mean for you, talk with your health care provider.

An RBC count is measured in millions per cubic millimeter (million/mm3). Normal values may vary slightly among different laboratories. One example of normal values is:

  • 3.6 to 5.0 million/mm3 for women

  • 4.2 to 5.4 million/mm3 for men

Your doctor can supply normal reference values.

An RBC that's lower than normal can be a sign of many health problems, including:

  • Anemia

  • Hodgkin lymphoma

  • Leukemia

  • Multiple myeloma

How is this test done?

The test requires a blood sample, which is drawn through a needle from a vein in your arm.

Does this test pose any risks?

Taking a blood sample with a needle carries risks that include bleeding, infection, bruising, or feeling dizzy. When the needle pricks your arm, you may feel a slight stinging sensation or pain. Afterward, the site may be slightly sore.

What might affect my test results?

Your RBC count could be affected by:

  • Dehydration

  • Overhydration

  • Stress

  • Altitude

  • Pregnancy

  • Some medications

  • Your position when the blood is drawn

How do I get ready for this test?

Your doctor may suggest that you avoid:

  • Exercising heavily

  • Being stressed

  • Becoming dehydrated

  • Drinking alcohol

  • Taking certain medications

Be sure your doctor knows about all medicines, herbs, vitamins, and supplements you are taking. This includes medicines that don't need a prescription and any illicit drugs you may use. 

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