Blood Transfusion

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Blood Transfusion


What is a blood transfusion?

Blood transfusion is a medical treatment that replaces blood lost through injury, surgery, or disease. The blood goes through a tube from a bag to an intravenous (IV) catheter and into your vein.

When is a blood transfusion needed?

You may need a blood transfusion if you lose too much blood, such as through:

If you have an illness in which your bone marrow doesn't make enough blood, such as aplastic anemia, you may need transfusions. Some diseases, such as hemophilia, prevent your body from making a needed blood component. Components are the different parts of blood, such as red blood cells, plasma, and platelets. You may need transfusions or injections of the missing blood component to help treat these diseases.

Is a blood transfusion safe?

Blood used for transfusions in Canada is very safe and generally free from disease. Donated blood is carefully tested. It is very rare to get a disease through a blood transfusion.

Getting the wrong blood type by accident is the main risk in a blood transfusion, but it is rare. Getting the wrong blood type happens in about 1 out of 14,000 transfusions.1 Transfusion with the wrong blood type can cause a severe reaction that may be life-threatening, but this is very rare.

Some people bank their own blood a few weeks before they have surgery. If they need a transfusion during surgery, they can receive their own banked blood. This reduces the risk of disease and transfusion reaction from donated blood.

If you have many blood transfusions, you are more likely to have problems from immune system reactions. A reaction happens when your body rejects the new blood and tries to attack parts of it. But tests can help avoid this. Before you get a blood transfusion, your blood is tested to find out your blood type. And the blood you will get in the transfusion is tested to make sure it matches your blood.

You may have a mild allergic reaction even if you get the correct blood type. Signs of a reaction include:

  • A fever.
  • Hives.
  • Shortness of breath.
  • Pain.
  • A fast heart rate.
  • Chills.
  • Low blood pressure.

A mild reaction can be scary, but it rarely is dangerous if it’s treated quickly.

What are blood types, and why are they important?

The most important blood type classification systems are the ABO system and the Rh system. A, B, AB, and O are the blood types in the ABO system. Each type of blood in the ABO system also has a positive or negative Rh factor. For example, if you have "A+ blood," it means your blood is type A in the ABO system and your Rh factor is positive.

If you get blood in a transfusion that isn't the right type, you may have a transfusion reaction. A mild transfusion reaction rarely is dangerous, but you must get treatment quickly. A severe transfusion reaction can be deadly.

How is blood collected?

Blood banks collect blood from volunteer donors. Before they donate, volunteers must answer questions about their current health, health history, and any diseases they may have been exposed to through travel to foreign countries, sexual behaviour, or drug use. Only people who pass this survey are allowed to donate blood.

Donated blood is then carefully tested for certain diseases and to find out the blood type. If there is any chance that the blood may not be safe to use, it is thrown away.

Most blood that passes the tests is then split into its components and sent out for use.

Blood and its components can be stored or used for only a short time before they must be thrown away. This is why blood banks are always looking for donors.

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Decision Points focus on key medical care decisions that are important to many health problems. Decision Points focus on key medical care decisions that are important to many health problems.
  Blood transfusions: Should I bank blood before surgery?

Uses of Blood Transfusion

Transfusions are used to treat blood loss or to supply blood components that your body cannot make for itself.

Treating blood loss

Blood loss may result from injury, major surgery, or diseases that destroy red blood cells or platelets, two important blood components. If too much blood is lost (low blood volume), your body cannot maintain a proper blood pressure, which results in shock. Blood loss can also reduce the number of oxygen-carrying red blood cells in the blood, which 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 have lost too many red blood cells or are not making enough of them, you are given packed red blood cells. If you have low blood volume, you are given plasma and/or other fluids to maintain blood pressure. If you have lost a great deal 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 does not make enough of them. For example, you may be given substances to help your blood clot (clotting factors) if you do not have enough of them naturally.

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

Replacing or supplementing blood components

One of the most common diseases that prevent the body from making an important blood component is hemophilia, an inherited disorder that affects the blood's ability to clot. Many factors are needed for the blood to clot properly. A person who has a bleeding disorder such as hemophilia is not able to make one of these clotting factors. Regular injections or transfusions with the missing clotting factor are needed to protect against uncontrolled bleeding in case of injury. Von Willebrand's disease is another inherited disorder that affects both clotting factors and platelets.

Another blood component that affects the blood's ability to clot is platelets. A reduced number of platelets (thrombocytopenia) or the failure of platelets to function properly increases the time it takes for bleeding to stop (increased bleeding time). Transfusion with platelets improves the clotting time, which reduces the risk of uncontrolled bleeding. This treatment does not 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, the oxygen-carrying substance in the red blood cells. There are several types of anemia, each with a different cause, and each is treated differently. Severe anemia may be treated with a transfusion of packed red blood cells. This temporarily increases the number of oxygen-carrying red blood cells in circulation and may improve symptoms, but it does not treat the cause of the anemia.

Blood Donation

Blood is donated by human volunteers, who can give blood as often as every 8 weeks. To donate blood, you must:

  • Be at least 17 years old.
  • Weigh at least 50 kg (110 lb).
  • Be in good health.

The process of blood donation and the handling of donated blood in Canada is regulated by Health Canada's Therapeutic Products Directorate (TPD). The TPD enforces five layers of overlapping safeguards to protect the blood supply against disease. These safeguards are implemented by Canadian Blood Services (CBS), the national organization that collects and distributes blood and blood products in all provinces and territories except Quebec. In Quebec, Héma-Québec performs this role.

  • Donor screening. To donate blood, you must answer a series of questions about your current health, health history, any travel to countries where certain diseases are common, and behaviour that increases your risk for getting certain diseases, such as drug use or unprotected sex. Your temperature, your blood pressure, and the volume of red blood cells in a blood sample (hematocrit) are checked. You may not be allowed to donate blood if any of these screening steps suggests a problem, such as potential exposure to an infectious disease or anemia.
  • 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 so that blood is not collected from them. The deferred-donor list includes people who have had certain types of cancer, had hepatitis after age 11, or are at high risk for HIV infection.
  • Blood testing. After donation, every unit of blood is tested for certain diseases, such as hepatitis B or C, HIV, West Nile virus, or HTLV-III virus. If any disease is detected, the blood is thrown away.
  • Quarantine. Donated blood is kept isolated from other blood and cannot be used for any purpose until it passes all required tests.
  • Quality assurance. Blood centres must keep careful records of every unit of donated blood. If a problem arises involving a donated unit of blood, the blood centre must notify the CBS and work with them to correct the problem.

Donating blood for your own use

If you are going to have surgery and expect to need a blood transfusion, you may want to consider donating or banking your own blood before the surgery (autologous donation). Many people consider this option to protect themselves from the risks of disease or mismatched blood associated with blood transfusion.

But autologous donation is not completely risk-free. Most problems that occur with any blood transfusion are the result of administrative errors that cause the wrong blood type to be given. These types of errors are rare but could cause you to receive blood other than the blood you banked before your surgery. It is also possible that banking blood before your surgery will increase the possibility that you will need a transfusion, because there was not enough time before the surgery for your body to replace all the blood you donated.

For more information on this option, see:

Click here to view a Decision Point. Blood transfusions: Should I bank blood before surgery?

Blood Types

Your blood is typed, or classified, according to the presence or absence of certain markers (antigens) found on red blood cells and in the plasma that allow your body to recognize blood as its own. If another blood type is introduced, your immune system recognizes it as foreign and attacks it, resulting in a transfusion reaction.

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, because they can receive any of the ABO types. People with type O blood are called universal donors, because their blood can be given to people with any of the ABO types. Mismatches with the ABO and Rh blood types are responsible for the most serious, sometimes life-threatening, transfusion reactions.

Rh system

The Rh system classifies blood as Rh-positive or Rh-negative, 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. Transfusion reactions caused by mismatched Rh blood types can be serious.

Minor blood types

There are over 100 other blood subtypes. Most have little or no effect on blood transfusions, but a few of them may be the main causes of mild transfusion reactions. Mild transfusion reactions are frightening, but they are rarely life-threatening when treated quickly.

Risks of Blood Transfusion

The risks of blood transfusions include transfusion reactions (immune-related reactions), non-immune reactions, and infections.

Immune-related reactions

Immune-related reactions occur when your immune system attacks components of the blood being transfused or when the blood causes an allergic reaction.

Most transfusion reactions occur because of errors made in matching the recipient's blood to the blood transfused. These administrative errors may occur because of mislabeled blood samples or misread labels. Much effort is made to prevent these errors; they occur in about 1 out of 14,000 transfusions.1 Even receiving the correct blood type sometimes results in a mild transfusion reaction.

These reactions may be mild or severe. Most mild reactions are not life-threatening when treated quickly. Even mild reactions, though, can be frightening. Severe transfusion reactions can be life-threatening, but this is very rare.

There are several immune-related transfusion reactions.

  • Non-hemolytic fever reactions cause fever and chills without destruction (hemolysis) of the red blood cells. This is the most common transfusion reaction. It can occur even when the blood has been correctly matched and administered. The more transfusions you receive, the greater your risk for this type of reaction. People who have had several transfusions are more likely to have non-hemolytic fever reactions or other types of immune system reactions. These problems occur because the body mistakes the new blood as harmful and makes specific antibodies to destroy it. Careful screening helps reduce the risk for these problems.
  • Hemolytic transfusion reactions destroy the transfused red blood cells when they are attacked by the person's immune system. This most commonly occurs if there is a mismatch with the ABO or Rh blood types, but some of the minor blood subtypes can also cause this severe reaction, which can be life-threatening.
  • An immune reaction to platelets in transfused blood results in the destruction of the transfused platelets. People who have this type of reaction may have difficulty finding blood that can be transfused without causing a reaction.
  • On rare occasions, an immune reaction may take place that attacks the person's lungs (transfusion-related acute lung injury). This results in difficulty breathing and other symptoms. Most people recover fully from this type of reaction.

Mild allergic reactions may involve itching, hives, wheezing, and fever. Severe reactions that involve anaphylactic shock can be life-threatening.

Doctors will stop a blood transfusion if they think you are having a reaction. A reaction may turn out to be mild. But at the beginning, it is hard for doctors to know whether it will be severe.

Non-immune reactions

Fluid overload is a common type of non-immune reaction.

  • Fluid overload can occur when you receive too much fluid through transfusions, especially if you have not experienced blood loss before the transfusion.
  • Fluid overload may require treatment with medicines to increase urine output (diuretics) to rid your body of the excess fluid.

Very rarely, a person can develop iron overload after having many repeated blood transfusions. This condition, sometimes called acquired hemochromatosis, is often treated with medicine. Too much iron can have an effect on many organs in the body.


The transmission of viral infections, such as hepatitis B or C or HIV, through blood transfusions has become very rare because of the safeguards enforced by Health Canada's Therapeutic Products Directorate (TPD) on the collection, testing, storage, and use of blood. The risk of infection from a blood transfusion is higher in less developed countries, where such testing may not happen and paid donors are used.

It is possible for blood, especially platelets, to become contaminated with bacteria during or after donation. Transfusion with blood that has bacteria can result in a systemic bacterial infection. Because of the precautions taken in drawing and handling donated blood, this risk is small. There is a greater risk for bacterial infection from transfusions with platelets. Unlike most other blood components, platelets are stored at room temperature. If any bacteria are present, they will grow and cause an infection when the platelets are used for transfusion.

Receiving a Blood Transfusion

Before you receive a blood transfusion, your blood is tested to determine your blood type. Blood or blood components that are compatible with your blood type are ordered by the doctor. This blood may be retested in the hospital laboratory to confirm its type. A sample of your blood is then mixed with a sample of the blood you will receive to check that no problems result, such as red blood cell destruction (hemolysis) or clotting. This process of checking blood types and mixing samples of the two blood sources is called typing and crossmatching.

Before actually giving you the transfusion, the doctor and nurses will each examine the label on the package of blood and compare it to your blood type as listed on your medical record. Only when all agree that this is the correct blood and that you are the correct recipient will the transfusion begin. Giving you the wrong blood type can result in a mild to serious transfusion reaction.

If you have banked your own blood in preparation for surgery (autologous donation), typing and crossmatching is not needed. But the doctors and nurses still examine the label to confirm that it is the blood you donated and that you are the right recipient. For more information on this option, see:

Click here to view a Decision Point. Blood transfusions: Should I bank blood before surgery?

Sometimes a doctor will recommend that you take acetaminophen (such as Tylenol), antihistamines (such as Benadryl), or other medicines to help prevent mild reactions, like a fever or hives, from a blood transfusion. Your doctor can treat more severe reactions as they occur.

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

Artificial Blood

Doctors hope to soon have artificial blood or blood replacements available. Blood replacements being studied include oxygen-carrying chemicals (such as perfluorocarbon emulsions) and cell-free hemoglobin—the portion of the red blood cell that carries oxygen. There are several advantages to blood replacements.

  • Blood replacement products can be stored for long periods of time. Human blood must be used within a few weeks of being donated.
  • Blood replacement products can be stored at room temperature. Human blood must be kept refrigerated until used.
  • There is no risk of a transfusion reaction caused by mismatched blood type.
  • Blood replacement products can be sterilized, eliminating the risk for infection.

The blood replacement products being tested still have problems. For example, blood replacement products can interfere with blood tests, are more quickly removed from the body, and are less efficient oxygen carriers.

Several of these products are being developed. But their use, after they are approved, will probably be limited to emergencies involving severe blood loss caused by serious accidents.

Other Places To Get Help


Phone: 1-888-666-HEMA (1-888-666-4362)
(514) 832-5000
Fax: (514) 832-1025
Web Address:

Héma-Québec's mission is to efficiently provide adequate quantities of safe, optimal blood components, substitutes, human tissues and cord blood to meet the needs of all Quebecers. Héma-Québec also provides expertise along with specialized and innovative services and products in the fields of transfusion medicine and human tissue transplantation.

Canadian Blood Services
1800 Alta Vista Drive
Ottawa, ON  K1G 4J5
Phone: 1-888-236-6238
(613) 739-2300
Fax: (613) 731-1411
Web Address:

Canadian Blood Services (CBS) is a not-for-profit, charitable organization, governed by the provincial and territorial Ministers of Health, whose sole mission is to manage the blood and blood products supply for Canadians. CBS collects approximately 800,000 units of blood annually; screens donors and tests blood or blood product collected for transmissible diseases; and processes them into the components and products that are administered to thousands of patients each year. CBS also manages the Unrelated Bone Marrow Donor Registry (UBMDR) to match donors for Canadian bone marrow transplant patients and for patients in other countries. CBS operates in all provinces and territories except Québec. In Québec, Héma-Québec ( performs this role.

KidsHealth for Parents, Children, and Teens
4600 Touchton Road East, Building 200
Suite 500
Jacksonville, FL  32246
Phone: (904) 232-4100
Fax: (904) 232-4125
Web Address:

This Web site is sponsored by Nemours Foundation. It has a wide range of information about children's health, from allergies and diseases to normal growth and development (birth to adolescence). This Web site offers separate areas for kids, teens, and parents, each providing age-appropriate information that the child or parent can understand. You can sign up to get weekly e-mails about your area of interest.

U.S. National Heart, Lung, and Blood Institute (NHLBI)
P.O. Box 30105
Bethesda, MD  20824-0105
Phone: (301) 592-8573
Fax: (240) 629-3246
TDD: (240) 629-3255
Web Address:

The U.S. National Heart, Lung, and Blood Institute (NHLBI) information center offers information and publications about preventing and treating:

  • Diseases affecting the heart and circulation, such as heart attacks, high cholesterol, high blood pressure, peripheral artery disease, and heart problems present at birth (congenital heart diseases).
  • Diseases that affect the lungs, such as asthma, chronic obstructive pulmonary disease (COPD), emphysema, sleep apnea, and pneumonia.
  • Diseases that affect the blood, such as anemia, hemochromatosis, hemophilia, thalassemia, and von Willebrand disease.



  1. Goodnough LT, et al. (2003). Transfusion medicine: Looking to the future. Lancet, 361(9352): 161–169.

Other Works Consulted

  • Beutler E (2006). Preservation and clinical use of erythrocytes and whole blood. In MA Lichtman et al., eds., Williams Hematology, 7th ed., pp. 2159–2173. New York: McGraw-Hill.
  • Goodnough LT (2008). Transfusion medicine. In L Goldman et al., eds., Cecil Medicine, 23rd ed., pp. 1324–1328. Philadelphia: Saunders Elsevier.
  • McCullough J (2006). Blood procurement and screening. In MA Lichtman et al., eds., Williams Hematology, 7th ed., pp. 2151–2158. New York: McGraw-Hill.
  • Vassallo R, Murphy S (2006). Preservation and clinical use of platelets. In MA Lichtman et al., eds., Williams Hematology, 7th ed., pp. 2175–2189. New York: McGraw-Hill.
  • Dzieczkowski JS, Anderson KC (2008). Transfusion biology and therapy. In AS Fauci et al., eds., Harrison's Principles of Internal Medicine, 17th ed., vol. 1., pp. 707–713. New York: McGraw-Hill Medical.
  • Galel SA, et al. (2009). Transfusion medicine. In JP Greer et al., eds., Wintrobe's Clinical Hematology, 12th ed., vol. 1, pp. 672–721. Philadelphia: Lippincott Williams and Wilkins.


By Healthwise Staff
Primary Medical Reviewer Anne C. Poinier, MD - Internal Medicine
Specialist Medical Reviewer Brian Leber, MDCM, FRCPC - Hematology
Last Revised February 26, 2010

This information does not replace the advice of a doctor. Healthwise, Incorporated disclaims any warranty or liability for your use of this information.