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:
- Injury or major surgery.
- An illness that causes bleeding, such as a bleeding ulcer.
- An illness that destroys blood cells, such as hemolytic anemia or thrombocytopenia.
Is a blood transfusion safe?
Blood used for transfusions in the United States is very safe and generally free from disease. Donated blood is carefully tested and tracked. 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. For every 1 million units of blood transfused, getting the wrong blood type happens, at the most, 4 times.footnote 1 Transfusion with the wrong blood type can cause a severe reaction that may be life-threatening.footnote 2
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 causes your body to form antibodies that attack the new blood cells. 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.
- Shortness of breath.
- A fast heart rate.
- 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 behavior, drug use, or needle sticks (such as from tattoos). 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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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 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.
Almost all of the blood used for blood transfusions is donated by volunteers.
For details on the donation process, see Donating Blood.
Safety of donated blood
The process of blood donation and the handling of donated blood in the United States is regulated by the U.S. Food and Drug Administration (FDA). The FDA enforces five layers of overlapping safeguards to protect the blood supply against disease.
- 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 behavior 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 viral 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 and C, HIV, West Nile virus, syphilis, and HTLV-I/II viruses. 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 centers must keep careful records of every unit of donated blood. If a problem arises involving a donated unit of blood, the blood center must notify the FDA 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).
For more information on this option, see:
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. But these types of reactions are rare.
For every 1 million units of blood transfused, getting the wrong blood type happens, at the most, 4 times.footnote 1 Transfusion with the wrong blood type can cause a severe reaction that may be life-threatening.footnote 2
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), nonimmune reactions, and infections.
Immune-related (transfusion) reactions
Immune-related reactions occur when your immune system attacks components of the blood being transfused or when the blood causes an allergic reaction. This is called a transfusion reaction.
Even receiving the correct blood type sometimes results in a 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.
Mild allergic reactions may involve itching, hives, wheezing, and fever. Severe reactions may cause anaphylactic shock.
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.
There are several immune-related transfusion reactions.
- Nonhemolytic 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 nonhemolytic 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 can cause the most serious problems, but these are rare. These reactions can occur when your ABO or Rh blood type and that of the transfused blood do not match. If this happens, your immune system attacks the transfused red blood cells. This can be life-threatening.
- Mild hemolytic transfusion reactions can happen when there is a mismatch of one of the more than 100 minor blood types. Most of the time, these reactions to the minor blood types are less serious than a mismatch of the ABO or Rh blood types.
- 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 trouble finding blood that can be transfused without causing a reaction.
- In rare cases, an immune reaction may take place that attacks the person's lungs (transfusion-related acute lung injury). This results in trouble breathing and other symptoms. Most people recover fully from this type of reaction.
Fluid overload is a common type of nonimmune 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.
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 the U.S. Food and Drug Administration (FDA) for 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 to be contaminated with bacteria or parasites. Bacterial contamination can happen during or after donation. Donated blood might have a parasitic infection. Transfusion with blood that has bacteria or parasites can result in a systemic infection. But this risk is small.
The risk of a bacterial infection in donated blood is small because of the precautions taken in drawing and handling blood. There is a greater risk of 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, a doctor or nurse will 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:
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 will treat a more severe reaction if one occurs.
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.
Experts are trying to create artificial blood or blood replacements. 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.
- Coil CJ, Santen SA (2011). Transfusion therapy. In JE Tintinalli, ed., Tintinalli's Emergency Medicine: A Comprehensive Study Guide, 7th ed., pp. 1493–1500. New York: McGraw-Hill.
- 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.
Current as of: April 12, 2023
Author: Healthwise Staff
Clinical Review Board: All Healthwise education is reviewed by a team that includes physicians, nurses, advanced practitioners, registered dieticians, and other healthcare professionals.
Current as of: April 12, 2023
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