Transfusion reaction is a problem that occurs after a patient receives blood. The immune system launches a response against the new blood cells or other parts of the transfusion.

The immune response protects the body from harmful substances. Foreign substances called antigens cause many immune responses. They trigger the production of proteins, called antibodies, which attach to antigens and help destroy them. They also trigger a type of white blood cell called lymphocytes, which recognize a certain antigen and destroy it.

The immune system normally can tell its own blood cells from other cells. On the surface of red blood cells are proteins that the body sees as antigens. In 1900, a German disease expert (pathologist), Karl Landsteiner, found 2 of these proteins, which he called A and B.

Blood is arranged by these antigens into blood types A, B, AB (contains both antigens), and O (contains neither antigen). The liquid part of blood (plasma) has antibodies against the opposite antigen. A person with Type A blood, for example, has antibodies against the B antigen.

In 1940, Dr. Landsteiner found another group of antigens. They were named Rhesus factors (Rh factors) because they were discovered during experiments on Rhesus monkeys.

People with Rhesus factors in their blood are called "Rh positive." Persons without the factors are called "Rh negative." Rh negative people form antibodies against the Rh factor if they are exposed to Rh positive blood.This can be a problem in an Rh negative mother who is pregnant with an Rh positive baby. There are other antigens too, besides ABO and Rh antigens.

Having antibodies against blood antigens makes blood groups compatible or incompatible. Tranfusing blood between compatible groups (such as O+ to O+) usually causes no problem. Blood transfusion between incompatible groups (such as A+ to O-) causes an immune response against the cells carrying the antigen. This can lead to a transfusion reaction.

The immune system attacks the donated blood cells, causing them to burst. This may cause serious symptoms, including kidney failure and shock. Antigens also occur in other parts of blood, including white blood cells, a type of blood cell called platelets, and plasma proteins.

These parts of the blood also cause a similar type of transfusion reaction. Or, antibodies in the transfused blood can bind to the patient's blood cells, causing a reaction.

Today, all blood is carefully screened. Modern lab methods and many checks have helped make transfusion reactions very rare.

• Fever
• Chills
• Rash
• Flank pain or back pain
• Bloody urine
• Fainting or dizziness

Symptoms of transfusion reaction usually appear during or right after the transfusion. Sometimes, they may develop after several days (delayed reaction). Symptoms may stay mild or progress to kidney failure, delayed anemia, or shock.

This disease may also change the results of these tests:

• RBC count
• Hemoglobin; serum
• Hemoglobin
• Hematocrit
• Haptoglobin
• Fibrin degradation products
• Coombs' test, indirect
• Coombs' test, direct
• CBC
• Bilirubin

Treatment can prevent or treat the severe effects of transfusion reaction. If symptoms occur during the transfusion, the transfusion is stopped. Blood samples from the person getting the transfusion (and from the donor blood) may be tested to tell whether symptoms are caused by transfusion reaction.

Mild symptoms may be treated based on the symptom. Drugs called antihistamines (such as diphenhydramine) treat the allergic reaction and may reduce itching and rash. The pain reliever, acetaminophen, can reduce fever and discomfort. Drugs called corticosteroids (such as prednisone or dexamethasone) reduce the immune response. Fluids given through a vein (intravenous) and other medications may be used to treat/prevent kidney failure and shock.

The outcome depends on how severe the reaction is. The disorder may disappear without problems. Or, it may be severe and life threatening.

• Discomfort
• Anemia
• Acute kidney failure
• Shock
• Lung dysfunction

Tell your health care provider if you are having a blood transfusion and you have had a reaction before.

Donated blood is put into ABO and Rh groups to reduce the risk of transfusion reaction.

Before a transfusion, patient and donor blood is often tested (crossmatched) to see if it is compatible. A small amount of donor blood is mixed with a small amount of patient blood. The mixture is checked under a microscope for signs of antibody reaction.

Hoffman R, Benz E, Shattil S, Furie B, Cohen H. Hematology: Basic Principles and Practice. 4th ed. Philadelphia, Pa: Churchill Livingstone, 2004.

McPherson RA, Pincus MR. Henry's Clinical Diagnosis and Management by Laboratory Methods. 21st ed. Philadelphia, Pa: Saunders, 2006.

Despotis GJ, Zhang L, Lublin DM. Transfusion risks and transfusion-related pro-inflammatory responses. Hematol Oncol Clin North Am. February 2007;21:147-161.