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. This is called a transfusion 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.²

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. 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.

Nonimmune reactions