Red Blood Cell (RBC) Count

What is a red blood cell (RBC) count?

A red blood cell (RBC) count measures the number of red blood cells, also known as erythrocytes, in your blood. Red blood cells carry oxygen from your lungs to every cell in your body. Your cells need oxygen to grow, reproduce, and stay healthy. An RBC count that is higher or lower than normal is often the first sign of an illness. So the test may allow you to get treatment even before you have symptoms.

Other names: erythrocyte count, red count

What is it used for?

A red blood cell (RBC) count is almost always part of a complete blood count, a group of tests that measure many different parts and features of your blood. The RBC measurement is used to help diagnose red blood cell disorders, such as anemia, a condition in which your body does not make enough healthy red blood cells.

Why do I need a red blood cell count?

You may get this test as part of a complete blood count, which is often included in a routine checkup. You may also need this test if you have symptoms of a low or high red blood cell count.

Symptoms of a low red blood cell count include:

• Weakness
• Fatigue
• Pale skin
• Rapid heartbeat

Symptoms of a high red blood cell count include:

• Headache
• Dizziness
• Vision problems

What happens during a red blood cell count?

A health care professional will take a blood sample from a vein in your arm, using a small needle. After the needle is inserted, a small amount of blood will be collected into a test tube or vial. You may feel a little sting when the needle goes in or out. This usually takes less than five minutes.

Will I need to do anything to prepare for this test?

You don't need any special preparations for a red blood cell (RBC) count.

Are there any risks to this test?

There is very little risk to having a blood test. There may be slight pain or bruising at the spot where the needle was put in, but most symptoms go away quickly.

What do the results mean?

Your results will show whether you have a normal red blood cell count or a count that is too low or too high.

A low red blood cell count can be a sign of:

• Anemia
• Leukemia, a type of blood cancer
• Malnutrition, a condition in which your body does not get the calories, vitamins, and/or minerals needed for good health
• Multiple myeloma, a cancer of the bone marrow
• Kidney failure

It may also be a sign of pregnancy.

A high red blood cell count can be a sign of:

• Dehydration
• Heart disease
• Polycythemia vera, a bone marrow disease that causes too many red blood cells to be made
• Scarring of the lungs, often due to cigarette smoking
• Lung disease
• Kidney cancer

If you have questions about your results, talk to your health care provider.

Learn more about laboratory tests, references ranges, understanding results.

Is there anything else I need to know about an RBC count?

If results showed you had a low or a high red blood cell count, you may need more tests to help make a diagnosis. These include:

• Reticulocyte count, a test that counts the number of reticulocytes in the blood. Reticulocytes are red blood cells that are still developing. These are also known as immature red blood cells.
• Iron tests, which measure iron levels in the blood. Iron is essential for making red blood cells.
• Vitamin B test, which measures the amount of one or more B vitamins in the blood. B vitamins are important for making red blood cells.