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.