Health Library Blood TransfusionFrom Healthwise

What is a blood transfusion?

Blood transfusion is a medical treatment to replace blood or portions of the blood lost through injury, surgery, or disease.

When is a blood transfusion needed?

A blood transfusion is needed if you have had significant blood loss or if your body cannot make or is losing an important component of blood.

Blood may be lost 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.
• An illness in which the bone marrow doesn't make enough blood, such as aplastic anemia.

Some diseases, such as hemophilia, prevent your body from making a needed blood component. Transfusions or injections of the missing blood component are used to treat these diseases.

Whole blood is rarely used for a blood transfusion, even when the transfusion is needed to treat blood loss. Usually, only certain components (blood fractions) are used for the transfusion. There are many fractions or components of blood, including red blood cells, plasma, a protein called albumin, platelets, and clotting factors.

Is a blood transfusion safe?

Although it is impossible to make the blood supply completely safe, blood transfusions given in the United States are very safe and generally free from disease. Blood collected for transfusion is carefully tested for disease-causing organisms. The transmission of a disease through a blood transfusion is very rare.

The main risk of a blood transfusion is that the wrong blood type may be accidentally given. This happens about once in every 14,000 transfusions.¹ Transfusion with the wrong blood type can result in a severe, sometimes life-threatening reaction.

A person who has had several blood transfusions is more likely to have problems from immune system reactions. This means problems occur because the person's body rejects and tries to attack parts of the new blood. But careful blood screening can lower the risk of these types of problems.

Even receiving the correct blood type can result in a mild transfusion reaction, causing fever, hives, shortness of breath, pain, rapid heart rate, chills, and low blood pressure. While a mild transfusion reaction is frightening, it is rarely life-threatening when treated quickly.

What are blood types, and why are they important?

Your blood type indicates specific markers (antigens) found on the red blood cells and in the plasma. These markers allow your body to recognize your blood as its own. If a different blood type is introduced, your immune system recognizes it as foreign and attacks it, resulting in a transfusion reaction. A mild transfusion reaction is rarely life-threatening, but it must be treated quickly. A severe transfusion reaction can be life-threatening.

The most important blood type classification systems are the ABO system and the Rh 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. Each type of blood in the ABO system 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.

There are over 100 other minor blood subtypes, which may sometimes cause minor transfusion reactions but rarely cause serious reactions.

How is blood collected?

Blood for transfusions is collected from volunteer donors by blood banks. The practice of paying donors for blood has been eliminated to ensure a safer blood supply. Before donating, volunteers must answer a survey about their current health, health history, and possible risk of disease exposure through travel to foreign countries, sexual behavior, or drug use. Only those people who pass this survey are allowed to donate blood.

After being collected, the blood is carefully tested for the presence of certain disease organisms and typed. If there is any suspicion that the blood may not be completely safe, it is discarded. Most blood that passes these tests is then broken down into its components (fractionated)—for example, into red blood cells, plasma, and platelets—before being distributed for use. Very little whole blood is used for transfusions.

Blood and its components can be stored or used for only a limited period of time before they must be discarded. This is why blood banks are constantly campaigning to recruit donors and encourage regular participation of their existing donors.

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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, reducing 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. While this temporarily increases the number of oxygen-carrying red blood cells in circulation and may improve symptoms, it does not treat the underlying cause of the anemia.

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 110 lb (50 kg).
• Be in good health.

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 hepatitis after age 11, or are at high risk for HIV infection.
• Blood testing. After donation, every unit of blood is tested for the presence of certain diseases, such as hepatitis B or C, HIV, West Nile virus, or HTLV-III virus. If any disease is detected, the blood is rejected.
• 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). 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 in preparation for the 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:

Should I bank blood before having surgery?

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.

The risks of blood transfusions include transfusion reactions (immune-related reactions), nonimmune 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 about once in every 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.

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.²
• 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 develop 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.

Nonimmune reactions

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.

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.

Infections

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) 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.

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:

Should I bank blood before having 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.

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.

Citations

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

2. Klein HG (2007). Transfusion medicine. In DC Dale, DD Federman, eds., ACP Medicine, section 5, chap. 10. New York: WebMD.

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 Textbook of 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 (2005). Transfusion biology and therapy. In DL Kasper et al., eds., Harrison's Principles of Internal Medicine, 16th ed., vol. 1., pp. 662–667. New York: McGraw-Hill.

• Goodnough LT, et al. (1999). Transfusion medicine: Blood conservation. New England Journal of Medicine, 340(7): 525–533.

• Goodnough LT, et al. (1999). Transfusion medicine: Blood transfusion. New England Journal of Medicine, 340(6): 438–447.

• Hillman RS, et al. (2005). Transfusion medicine. In Hematology in Clinical Practice, 4th ed., pp. 431–440. New York: McGraw-Hill.

Author:	Caroline Rea, RN, BS, MS	Last Updated: December 27, 2007
Medical Review:	Anne C. Poinier, MD - Internal Medicine Joseph O'Donnell, MD - Hematology/Oncology
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