Red Blood Cells

Author: Courtney Misher, MPH, BS R.T.(T)
Content Contributor: Allyson Van Horn, MPH
Last Reviewed: November 26, 2024

Blood is made up of four parts:

  • Red blood cells.
  • White blood cells.
  • Platelets.
  • Plasma.

What are red blood cells?

A red blood cell is the part of your blood that makes it red. Hemoglobin is the protein that makes up red blood cells. Red blood cells carry oxygen from your lungs to the cells in your body. Red blood cells also move carbon dioxide back to your lungs where it is exhaled (breathed out).

Red blood cells are made in the bone marrow, which is found inside your bones. They live for about 120 days. Eating foods rich in iron and vitamins, such as E, B2, B12, and B3, helps to maintain healthy red blood cells.

What is a normal red blood cell count?

A normal red blood cell count is between 12 to 18 g/dL (grams per deciliter). Your red blood cell count can be checked by drawing blood for a complete blood count (CBC). A CBC measures the levels of the components that make up your blood.

What causes a low red blood cell count?

There are a few medical issues that can lead to a low red blood cell count, also called anemia. There are many types and causes of anemia. Some cancers can cause internal bleeding, which leads to blood loss, and sometimes anemia. Cancers that start in the bone marrow, such as leukemia, can affect the way your blood is produced.

Chemotherapy and radiation therapy (common cancer treatments) can affect not just cancer cells, but also healthy cells. Because of this, both treatments can lead to anemia.

If you have anemia, you may feel very tired, look pale, or feel short of breath.

How is anemia treated?

Anemia can be treated by having a red blood cell transfusion. This is when red blood cells are given through an intravenous (IV) line.

Who needs a red blood cell transfusion?

If your hemoglobin level is well below normal (often below 8g/dL), you may be given a transfusion. If you have a heart condition and your hemoglobin is low but not below 8g/dL, your care team may choose to give you a transfusion. Blood transfusions are also used during surgery when there is blood loss.

The transfusion increases the number of red blood cells in your body. These cells can then help carry more oxygen throughout your body. This will give you more energy and help treat symptoms like pale color and shortness of breath.

How is a red blood cell transfusion done?

Before having a blood transfusion, your blood type will be checked, which is done by having your blood drawn. Blood type is determined by which antigens are found in your blood. Blood that you get will be checked to make sure it is a match for your blood. This is done in a laboratory that specializes in blood products.

The infusion of the blood you are getting starts slowly and your vital signs (temperature, heart rate, oxygenation, and blood pressure) are checked often to make sure that you are not having a reaction to the transfusion. The rate that the blood is infusing may be increased if you are not having a reaction. A blood transfusion can take a few hours.

What are the risks of having a red blood transfusion?

Although not common, there are risks to having a red blood cell transfusion. These include infection and reactions. If you start to have itching, chills, any new pain, nausea, trouble breathing, or your throat feels tight, let your care team know right away as these are symptoms of a reaction.

The blood you get is collected from donors. All donated blood is tested for viruses, bacteria, and parasites. The risk of catching a virus or other infection from a blood transfusion is very low. This includes HIV and Hepatitis B and C.

If you are having signs of anemia, you should call your healthcare provider so that your blood can be tested. Ask your healthcare provider if you have any questions about anemia or having a transfusion.

American Cancer Society (2024). Low Red Blood Cell Counts (Anemia).

American Cancer Society (2023). Kinds of Blood Product Transfusions.

American Red Cross (n.d.). Blood Transfusion Process.

National Cancer Institute (n.d.) Red Blood Cell.

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