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Blood Transfusion

Treatment Overview

Blood transfusion is a medical treatment to replace the blood or parts of blood that your body has lost. The blood goes through a tube from a bag to an intravenous (I.V.) catheter and into your vein.

You may need a blood transfusion after losing blood from an injury, a major surgery, an illness that causes bleeding, or an illness that destroys blood cells.

Transfusions are also used to give you the parts of blood—such as platelets, plasma, or substances that cause clotting—that your body needs to fight an illness or stop bleeding.

Safety of donated blood

Almost all of the blood used for blood transfusions is donated by volunteers.

The process of blood donation and the handling of donated blood is regulated by Health Canada. It enforces several ways to protect the blood supply from disease.

Donor screening.

To donate blood, you must answer questions about your health history, any travel to countries where certain diseases are common, and any behaviour that increases your risk for certain diseases, such as drug use or unprotected sex. To be sure you are in good health to donate, your temperature, blood pressure, and the protein in your red blood cells (hemoglobin) are checked. You may not be allowed to donate blood if any of these screening steps suggests a problem.

Deferred-donor lists.

Organizations that collect blood must keep lists of people who are permanently prevented from giving blood. Potential donors must be checked against this list.

Blood testing.

After donation, every unit of blood is tested for certain diseases. These include hepatitis B and C, HIV, West Nile virus, syphilis, and HTLV-I/II viruses. If any disease is found, the blood is thrown away.


Donated blood is kept isolated from other blood. It can't be used until it passes all required tests.

Quality assurance.

Blood centres must keep careful records of all donated blood. If there is a problem, the blood centre must tell Health Canada and work with them to correct the problem.

Why It Is Done

Transfusions are done to treat blood loss. They are also used to give your body the parts of blood (called components) that your body can't make for itself.

Treating blood loss

Blood loss may be caused by injury, major surgery, or diseases that destroy red blood cells or platelets. Red blood cells and platelets are two important components from your blood. If too much blood is lost (low blood volume), your body can't maintain a proper blood pressure. This lack of pressure causes shock. Blood loss can also reduce the number of oxygen-carrying red blood cells in the blood. Fewer red blood cells may prevent enough oxygen from reaching the rest of the body.

Whole blood is rarely given to treat blood loss. Instead, you are given the blood component you most need. If you've lost too many red blood cells or aren't making enough of them, you are given packed red blood cells. If you have low blood volume, you are given other fluids to maintain blood pressure. If you've lost a lot of blood, or if your clotting factors or platelets are low or abnormal, you may also need a transfusion of either of these to help control bleeding. Sometimes you may need replacements of some blood substances if your body doesn't make enough of them. For example, you may be given substances to help your blood clot.

Blood lost during surgery sometimes can be cleaned and returned to you as a transfusion. This greatly reduces the amount of donated blood you might need. Receiving your own blood back is safer. That's because there is no chance of a reaction.

Replacing or supplementing blood components

One blood component that affects how well the blood can clot is platelets. Having too few platelets (thrombocytopenia) or the failure of platelets to work as they should increases the time it takes for bleeding to stop. (This is called increased bleeding time.) Transfusion with platelets improves the clotting time, which reduces the risk of uncontrolled bleeding. This treatment doesn't cure the cause of platelet loss.

Anemia is a decrease in the number of oxygen-carrying red blood cells or a decrease in the amount of hemoglobin. Hemoglobin is a substance in the red blood cells that carries oxygen. There are several types of anemia. Each type has a different cause, and each is treated differently. Severe anemia may be treated with a transfusion of packed red blood cells. This increases the number of oxygen-carrying red blood cells for a short time. And it may improve symptoms. But it doesn't treat the cause of the anemia.

How It Is Done

Before you receive a blood transfusion, your blood is tested to find out what your blood type is. Blood or blood parts that are a match with your blood type are ordered by your doctor. Blood is typed as A, B, AB, or O. It is also typed as Rh-positive or Rh-negative.

Your blood is also screened to look for antibodies that might react with the blood that is given to you. The blood you are getting is checked and rechecked to make sure that it's the right type for you.

A sample of your blood is mixed with a sample of the blood you will receive to check for problems. Before actually giving you the transfusion, a doctor and nurses will look at the label on the package of blood and compare it to your hospital ID bracelet and medical records. The transfusion begins only when all agree that this is the correct blood and that you are the correct person to receive it.

To receive the transfusion, you will have an intravenous (I.V.) catheter inserted into a vein. A tube connects the catheter to the bag containing the blood, which is placed higher than your body. The blood then flows slowly into your vein. A doctor or nurse will check you several times during the transfusion to watch for a reaction or other problems.

Blood types

Your blood is typed according to the presence or absence of certain markers called antigens. Antigens are found on red blood cells and in the plasma. They allow your body to recognize blood as its own. If another blood type enters your body, your immune system recognizes it as foreign and attacks it.

ABO blood type system

The ABO system consists of A, B, AB, and O blood types. People with type A have antibodies in the blood against type B. People with type B have antibodies in the blood against type A. People with AB have no anti-A or anti-B antibodies. People with type O have both anti-A and anti-B antibodies. People with type AB blood are called universal recipients. They can receive any of the ABO types. People with type O blood are called universal donors. Their blood can be given to people with any of the ABO types.

Rh system

The Rh system classifies blood as Rh-positive or Rh-negative. It's based on the presence or absence of Rh antibodies in the blood. People with Rh-positive blood can receive Rh-negative blood. But people with Rh-negative blood will have a transfusion reaction if they receive Rh-positive blood.

Minor blood types

There are over 100 other blood subtypes. Most have little or no effect on blood transfusions.


Blood transfusions have many benefits and are often life-saving. But they also have a few risks. Possible risks include:

  • Your body's reaction to receiving new blood. This may include:
    • Fever.
    • Breathing problems.
    • Allergic reaction, such as hives, swelling, or a new rash.
  • An infection from the blood. This risk is small because of the strict rules placed on handling and storing blood. Getting a viral infection, such as HIV or hepatitis B or C, through blood transfusions has become very rare. Health Canada enforces strict guidelines on the collection, testing, storage, and use of blood.
  • Getting the wrong blood type. Severe reactions, which can be life-threatening, are very rare.
  • An infection at the transfusion site, such as redness, swelling, pain, bleeding, or pus.


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