The immune system never rests; its cells constantly patrol the circulation. Without the immune system, the body would be overwhelmed with infections.

If incompatible blood is given in a transfusion, the donor cells are treated as if they were foreign invaders, and the patient’s immune system attacks them accordingly. Not only is the blood transfusion rendered useless, but a potentially massive activation of the immune system and clotting system can cause shock, kidney failure, circulatory collapse, and death.


Some people need transfusions because they have lost blood during surgery or in an injury, while others have medical conditions such as sickle cell anemia or cancer that affect their blood.

If the recipient and the donor have exactly the same type of blood, the transfusion will not cause a reaction. The problem occurs when proteins called antibodies in the recipient’s blood match another type of proteins called antigens in the donor’s blood. The donor’s red blood cells clump in the recipient’s body, clogging the blood vessels and preventing blood from flowing into various parts of the body. The donor’s red blood cells also break open, releasing a substance called hemoglobin that becomes toxic when it escapes from the cells. The resulting reaction usually happens suddenly during the transfusion, but delayed reactions can also occur.

Signs and symptoms may include anxiety, trouble breathing, fever, chills, flushing of the face or severe pain, especially in the lower back. If the person goes into shock, the skin will become cold and clammy, the blood pressure will drop, and the pulse will be rapid and feeble. Later, the person’s skin and the whites of the eyes may become yellowed, a condition called jaundice. The severity of the signs and symptoms depend on a number of factors, including how much blood the person received, how fast the blood was flowing, and the condition of the recipient’s heart, kidneys and liver.


The first step in treatment is to stop the transfusion as soon as signs and symptoms begin. That unit of blood is sent back to the blood bank for testing, and any other blood products waiting for transfusion into the same patient are cancelled. The recipient’s blood and urine will be tested to determine if red blood cell damage is causing the signs and symptoms and, if so, whether or not the kidneys have been affected.

A person who receives incompatible blood through a transfusion may have a delayed reaction within one to four weeks afterward. If the reaction is mild, there may be no symptoms at all, or the recipient may have a low fever. Sometimes the only indication of a delayed reaction is found when the health care provider does follow-up blood tests and finds that the person’s blood count is lower than expected. Frequent follow up checks at the doctor is essential for your health after you have undergone a blood transfusion.