Transfusions are given to increase the blood's ability to carry oxygen, restore the amount of blood in the body (blood volume), and correct clotting problems. Transfusions are usually safe, but sometimes people have adverse reactions.
To minimize the chance of an adverse reaction during a transfusion, health care practitioners take several precautions. Before starting the transfusion, usually a few hours or even a few days beforehand, the person is cross-matched with the donor blood (not done for transfusions of plasma or platelets).
After double-checking labels on the bags of blood that are about to be given to ensure the units are intended for that recipient, the health care practitioner gives the blood to the recipient slowly, generally over 1 to 4 hours for each unit of blood. Because most adverse reactions occur during the first 15 minutes of the transfusion, the recipient is closely observed at first. After that, a nurse checks on the recipient periodically and must stop the transfusion if an adverse reaction occurs.
Most transfusions are safe and successful. However, mild reactions occur occasionally, and, rarely, severe and even fatal reactions may occur.
The most common reactions, which occur in 1 to 2% of transfusions, are
The most serious reactions are
Rare reactions include
Graft-versus-host disease (whereby transfused cells attack the cells of the person receiving a transfusion)
Complications of massive transfusion (poor blood clotting, low body temperature, and low calcium and potassium levels)
Fever may be caused by a reaction to the transfused white blood cells or to chemicals (cytokines) released by the transfused white blood cells. For this reason, most hospitals in the United States remove white blood cells from the transfused blood after it is collected.
In addition to an increase in temperature, the person has chills and sometimes headache or back pain. Sometimes the person also has symptoms of an allergic reaction such as itching or a rash.
Usually, acetaminophen to reduce fever is the only treatment needed. People who have had a fever and need another transfusion may be given acetaminophen before the next transfusion.
Symptoms of an allergic reaction include itching, a widespread rash, swelling, dizziness, and headache. Less common symptoms are breathing difficulties, wheezing, and airway obstruction. Rarely, an allergic reaction is severe enough to cause low blood pressure and shock.
If an allergic reaction occurs, the transfusion is stopped and the person is given an antihistamine. More serious allergic reactions may be treated with hydrocortisone or even with epinephrine.
Treatments are available that allow transfusions to be given to people who previously had allergic reactions to them. People who have repeated, severe allergic reactions to donated blood may have to be given washed red blood cells. Washing the red blood cells removes components of the donor blood that may cause allergic reactions. Because white blood cells and platelets are filtered out of donated blood before it is stored (a process called leukocyte reduction), allergic reactions are less common now.
Transfusion recipients can receive more fluid than their body can easily handle. Too much fluid may cause swelling throughout the body or difficulty breathing. This complication is the most common cause of transfusion-related death. Recipients who have heart disease are most vulnerable, so their transfusions are given more slowly and they are monitored closely. People who receive too much fluid are given a drug to help the body remove fluid (a diuretic).
Another very rare reaction, called transfusion-related acute lung injury (TRALI), is caused by antibodies in the donor's plasma. This reaction may cause serious breathing difficulties. This complication is the second most common cause of transfusion-related death. It occurs in 1 in 5,000 to 1 in 10,000 cases, but many cases are mild and so may not be diagnosed. Most people with mild to moderate lung injuries are given oxygen and other treatments that aim to support breathing until the lungs heal. Using plasma donated by men reduces the risk of having this reaction.
Despite careful typing and cross-matching of blood, mismatches due to subtle differences between donor and recipient blood (and, very rarely, errors) can still occur. When such a mismatch occurs, the recipient's body destroys the transfused red blood cells (a hemolytic reaction) shortly after the transfusion.
Usually, this reaction starts as general discomfort or anxiety during or immediately after the transfusion. Sometimes breathing difficulty, chest pressure, flushing, and severe back pain develop. Sometimes the person has cold, clammy skin and low blood pressure (shock). Very rarely, the person may die.
As soon as doctors suspect a hemolytic reaction, they stop the transfusion. Doctors give treatment to support the person's breathing and blood pressure. Doctors do blood and urine tests to confirm that red blood cells are being destroyed.
Sometimes a hemolytic reaction is delayed, occurring within the month after a transfusion. Usually, such a reaction is mild and may only be noticed when blood tests are done to monitor the person's recovery from the disorder that necessitated the transfusion. These reactions occur due to the presence of an uncommon blood group antigen in the donor blood that are not routinely tested for.
Graft-versus-host disease is an unusual complication that affects primarily people whose immune system is impaired by drugs or disease. In this disease, donated white blood cells (the graft) attack the recipient's (host's) tissues. The symptoms include fever, rash, low blood pressure, fewer blood cells than normal (low blood counts), tissue destruction, and shock. These reactions can be fatal. However, graft-versus-host disease can be eliminated by giving people with a weakened immune system red blood cells and platelets that have been treated with radiation.
Despite careful testing and storage of blood products, infectious organisms are sometimes transmitted during a transfusion. Testing of blood and careful evaluation of blood donors keep transmission of infectious organisms low. However, sometimes testing does not detect organisms in blood from a donor who was very recently infected or infected by an organism for which there is no test.
Massive transfusion is transfusing a volume of blood equal to the person's total blood volume (about 10 units in an average adult) in a period of 24 hours or less. Such transfusion is sometimes necessary after a severe injury or during certain surgical procedures. The main complications of massive transfusion are poor blood clotting (coagulopathy) and a low body temperature (hypothermia).
Blood clotting is impaired because the transfused blood does not contain enough of the substances (clotting factors and platelets) that help blood clot. Thus, if doctors think people are likely to require a large volume of transfused blood, fresh frozen plasma and platelets are also transfused. Fresh frozen plasma contains clotting factors.
Sometimes, massive transfusion can cause hypocalcemia (low calcium level in the blood) and/or hypokalemia (low potassium level in the blood). Very low calcium levels can cause symptoms such as muscle spasms (tetany) and abnormal heart rhythms. Very low potassium levels can cause muscle weakness and abnormal heart rhythms.
Because blood is refrigerated while in storage, transfusion of many units of blood may result in a low body temperature. To prevent a low body temperature due to massive transfusion, doctors use a special device that gently warms the blood as it passes through the intravenous tubing.