Getting a Blood Transfusion

A blood transfusion is given through tubing connected to a needle or fine tube (catheter) that’s in a vein. The amount and part of the blood transfused depends on what the patient needs.

First, blood tests such as a complete blood count (CBC) are done to find out if the patient’s symptoms are likely to be helped by a transfusion. A CBC measures the levels of components within the blood such as red blood cells, white blood cells, and platelets. Tests of clotting (coagulation) may also be done if abnormal bleeding is a problem.

If a transfusion is needed, it must be prescribed by a health care provider. At that point, more blood tests must be done to find a donated blood component that closely matches the patient.

Blood types

Blood types are important when it comes to transfusions. If you get a transfusion that does not work with your blood type, your body’s immune system could fight the donated blood. This can cause a serious or even life-threatening transfusion reaction. (See “Possible risks of blood transfusion.”)

To be sure no mistakes are made, donated blood is carefully tested to find out what type it is. This is done when it’s taken from the donor and again once it’s received by the hospital lab. The blood bag is labeled with the type of blood it contains. When a person needs a blood transfusion, a blood sample is drawn from them and tested the same way.

All blood has the same components, but not all blood is the same. People have different blood types, which are based on substances called antigens on a person’s blood cells. The 2 most important antigens in blood typing are called A, B, O, and Rh.

  • Each person has an ABO blood type – either A, B, AB, or O – which means antigen A, antigen B, both antigens (type AB), or neither antigen (type O) is found on their blood cells.
  • Each person also is either Rh-positive or Rh-negative (you either have Rh or you don’t). 

These 2 factors can be combined into 8 possible blood types:

A positive

B positive

AB positive

O positive

A negative

B negative

AB negative

O negative

ABO blood types

Two antigens on blood cells (A and B) determine a person’s ABO blood type (either A, B, AB, or O). In the United States, the most common blood type is O, followed closely by type A.

  • If you have type O blood, you can only get type O red blood cell transfusions. But you can give your red blood cells to people with type A, B, AB, or O blood, which is why you are sometimes called a universal donor. (Universal donor blood cells are typically only used in emergencies. For example, if a person is bleeding severely and nearing death, there may no time for testing. In everyday practice, people in the US are almost always given the exact same type of red blood cells that they have.)
  • If you have type A blood, you cannot get either type B or AB red blood cells.
  • If you have type B blood, you cannot get type A or AB red blood cells.
  • If you have type AB blood, you can get transfusions of O, A, B, or AB red blood cells.

Rh factor

Blood is either Rh-positive or Rh-negative, depending on whether the red blood cells have Rh antigens on their surface. A person who has type B, Rh-positive blood is called B positive, whereas a person with type B, Rh-negative blood is B negative.

If you have Rh-positive blood, you can get Rh-positive or Rh-negative red blood cell transfusions. But people with Rh-negative blood should only get Rh-negative red blood cells except in extreme emergencies. This is because an Rh-positive blood transfusion can cause a person with Rh negative blood to make antibodies against the Rh factor, causing a transfusion reaction (discussed below). If an Rh-negative woman makes antibodies like this, it can seriously harm any Rh-positive babies she may have in the future. Her anti-Rh antibodies can attack Rh-positive blood cells in the fetus.

Other antigens

There are other antigens on red blood cells that can lead to transfusion reactions. These are rare because people don’t make antibodies against them unless they have had transfusions before. Still, these antigens may become a factor in matching blood for a person who has had many transfusions in the past, as is the case for some people with cancer.

Plasma, platelets, cryo, and blood type

Blood  types are also important for plasma transfusions, but the rules are different than the rules for red blood cells transfusions. For example, people with type AB blood are universal plasma donors, and they can only receive type AB plasma.

For platelet and cryoprecipitate transfusions, matching the blood type of the donor to the recipient is usually not critical, but labs still try to match them. This may become important for patients who have already had many transfusions or who have reacted to transfusions in the past.

Antibodies and cross-matching

After blood is typed, a test called an antibody screen is done to see if a patient’s plasma contains other antibodies besides those against A, B, and Rh. If there are extra antibodies, the cross-matching may take longer. This is because some units of donor blood may not fully match the recipient’s, even though they have the same ABO and Rh types.

Before a person can get a transfusion of red blood cells, another lab test called a cross-match must be done to make sure that the donor blood is compatible with the recipient’s.

A unit of the right ABO and Rh type blood is selected, and a drop of donor red cells from the unit is mixed with a drop of plasma from the patient. The mixture is watched to see if the patient’s plasma causes the donor blood cells to clump. This may happen if the patient has extra antibodies to a protein in the donor unit. If there are no problems (no clumping), a cross-match takes about 30 minutes.

A cross-match is usually not needed for a platelet or plasma transfusion unless the platelets look like they could contain some red blood cells.

The transfusion process

Most blood transfusions are given in the hospital or in outpatient clinics.

Red blood cell transfusions are usually started slowly while the patient is watched closely for the signs and symptoms of a transfusion reaction. The patient’s vital signs (such as temperature, heart rate, and blood pressure) are checked often. If there are no problems, the infusion rate will slowly be increased (so the blood goes in faster). Each unit of red blood cells is usually given over a couple of hours, and should be completed within 4 hours. Other blood products, like plasma and platelets, go in much faster.

A visiting nurse can give transfusions and monitor patients in their homes. Home transfusions follow the same safety standards as hospital transfusions. A health care provider must be sure that a patient’s health is stable for transfusion at home. Emergency medical care must be available close by in case it is needed. And the blood must be kept within a certain temperature range while being taken to the home.

Possible risks of blood transfusions

Although blood transfusions can be life-saving, they are not without risks. Infections were once the main risk, but they have become extremely rare with testing and donor screening. Transfusion reactions and other non-infectious problems are now more common than infections.

When you are getting a transfusion of any kind, it’s very important that you let your nurse know right away if you notice any changes in how you feel, such as itching, shivering, headache, chest or back pain, throat tightness, nausea, dizziness, trouble breathing, or other problems. You should report any changes that happen in the next few days, too.

Transfusion reactions

Blood transfusions sometimes cause transfusion reactions. There are several types of reactions and some are worse than others. Some reactions happen as soon as the transfusion starts, while others take several days or even longer to develop.

Many precautions are taken before a transfusion is started to keep reactions from happening. The blood type of the unit is checked many times, and the unit is carefully matched to be sure that it matches the blood type and Rh factor of the person who will get it. After that, both a nurse and blood bank lab technician look at the information about the patient and the information on the unit of blood (or blood component) before it’s released. The information is double-checked once more in the patient’s presence before the transfusion is started.

Allergic reaction

This is the most common reaction. It happens during the transfusion when the body reacts to plasma proteins or other substances in the donated blood. Usually the only symptoms are hives and itching, which can be treated with antihistamines like diphenhydramine (Benadryl). In rare cases these reactions can be more serious.

Febrile reaction

The person gets a sudden fever during or within 24 hours of the transfusion. Headache, nausea, chills, or a general feeling of discomfort may come with the fever. Acetaminophen (Tylenol) may help these symptoms.

These reactions are often the body’s response to white blood cells in the donated blood. They are more common in people who have had transfusions before and in women who have been pregnant several times. Other types of reaction can also cause fever, and further testing may be needed to be sure that the reaction is only febrile and not something more serious.

Patients who have had febrile reactions or who are at risk for them are usually given blood products that are leukoreduced. This means that the white blood cells have been removed by filters or other means. People with cancer often get leukoreduced blood products.

Transfusion-related acute lung injury

Transfusion-related acute lung injury (TRALI) is a rare but very serious transfusion reaction. It can happen with any type of transfusion, but is much more likely in people who are already seriously ill. Transfusions that contain more plasma, such as fresh frozen plasma or platelets, seem more likely to result in TRALI. It often starts within 1 to 2 hours of starting the transfusion, but can happen anytime up to 6 hours after a transfusion. There’s also a delayed TRALI syndrome, which can begin up to 72 hours after the transfusion is given.

The main symptom of TRALI is trouble breathing, which can become life-threatening. If TRALI is suspected during a transfusion, the transfusion should be stopped right away.

Doctors now believe that several factors are involved in this illness. Many of the patients who get TRALI have had recent surgery, trauma, cancer treatment, transfusions, or have an active infection. Most of the time, TRALI goes away within 2 or 3 days if the person is helped with oxygen, fluids, and sometimes a breathing machine. Even with this kind of treatment, it’s deadly in 5% to 10% of cases. TRALI is more likely to be fatal if the patient was already very ill before the transfusion.

Delayed TRALI has been observed in people who are already critically ill or seriously injured. These patients have a higher risk of death. If a patient who has had TRALI in the past needs red blood cells, doctors may try to prevent it by removing most of the plasma from the red blood cells or by taking other measures. Researchers are working on other ways to reduce the risk of TRALI.

Acute immune hemolytic reaction

An acute hemolytic reaction is the most serious type of transfusion reaction, but careful blood handling has helped make it very rare. It happens when donor and patient blood types do not match. The patient’s antibodies attack the transfused red blood cells, causing them to break open (hemolyze) and release harmful substances into the bloodstream.

Patients may have chills, fever, chest and lower back pain, and nausea. The kidneys may be badly damaged, and dialysis may be needed. A hemolytic reaction can be deadly if the transfusion is not stopped as soon as the reaction starts.

Delayed hemolytic reaction

This type of reaction happens when the body slowly attacks antigens (other than ABO antigens) on the transfused blood cells. The blood cells are broken down days or weeks after the transfusion. There are usually no symptoms, but the transfused red blood cells are destroyed and the patient’s red blood cell count falls. In rare cases, the kidneys may be affected, and treatment may be needed.

People don’t usually have this type of reaction unless they have had many transfusions in the past. Those who do have this reaction need special blood tests before any more blood can be transfused. Units of blood that do not have the antigen that the body is attacking must be used.

Graft-versus-host disease

Graft-versus-host disease (GVHD) can occur when a person with a very weak immune system gets a transfused blood product that contains white blood cells. The white cells in the transfusion attack the tissues of the patient who got the blood.

Within a month of the transfusion, the patient may have fever, liver problems, rash, and diarrhea.

To prevent white blood cells from causing GVHD, donated blood can be treated with radiation before transfusion. (Radiation stops white blood cells from working but does not affect red blood cells.) These are called irradiated blood products. They are often used for people with cancer.


Blood transfusions can transmit infections caused by bacteria, viruses, and parasites. The chance of getting an infection from blood in the United States is extremely low, but the exact risk for each infection varies. Testing units of blood for infection and asking questions to learn about donor risks has made the blood supply very safe. Still, no test or set of questions is 100% accurate.

Bacterial contamination

Rarely, blood gets contaminated with tiny amounts of skin bacteria during donation. Platelets are the most likely blood component to have this problem because platelets must be stored at room temperature. Other components are refrigerated or frozen which curbs the growth of bacteria.

Blood banks now routinely test platelets and destroy units that are likely to cause harm. The tests are still being refined, but today fewer cases of illness are caused by platelets. Also, more hospitals use single donor platelets, which have a lower risk of bacterial contamination than pooled platelets.

Hepatitis B and C viruses

Several steps are routinely taken to reduce the risk of viral hepatitis from blood transfusion. People who are getting ready to donate blood are asked questions about hepatitis risk factors and symptoms of hepatitis. Donated blood is also tested for infection from hepatitis B virus, hepatitis C virus, and other liver problems that could be signs of other types of hepatitis.

Viral hepatitis infection transmitted by blood transfusions is rare. The risk of getting hepatitis B from a blood transfusion in the US is about 1 in 800,00 to 1 in 1 million. The risk of getting hepatitis C is about 1 in 1 million.

Work continues to be done to reduce the risk of these infections even further.

Human immunodeficiency virus (HIV)

Human immunodeficiency virus (HIV) causes acquired immune deficiency syndrome (AIDS). Testing each unit of donated blood for HIV began in 1985, and all donated blood is now tested for HIV with 2 screening tests.

With improved testing for HIV, the number of transfusion-related AIDS cases continues to drop. The risk of HIV transmission from a transfusion is estimated to be about 1 in 1 million to 1 in 1.5 million. Along with testing, the risk is reduced by asking donors questions about HIV risk factors and symptoms.

Cytomegalovirus (CMV)

Cytomegalovirus (CMV) is a very common infection in the United States. Up to 3 in 4 people have this infection by the age of 40. Most people with CMV don't know they have it because it rarely causes serious symptoms. Still, because it doesn’t cause problems for most people, donated blood is not always tested for CMV.

If you haven’t had CMV and your immune system is weakened, being exposed to CMV can make you very ill. CMV spreads from person to person through body fluids like blood, saliva, urine, semen, and breast milk. If you haven’t had CMV and you need a transfusion, your cancer team might choose to give you CMV-negative blood products, which come from CMV-negative donors. Or they might use blood products prepared with fewer white blood cells in which the virus lives. Either of these measures greatly reduces the risk of getting CMV if your immune system is weak.

Other infections

Along with the tests noted above, all blood for transfusion is tested for syphilis, as well as HTLV-I and HTLV-II (viruses linked to human T-cell leukemia/lymphoma). Since 2003, donated blood has been tested for the West Nile virus, too. In 2007, blood banks also began testing for Chagas disease (common in South and Central America).

Diseases caused by certain bacteria, viruses, and parasites, such as babesiosis, malaria, Lyme disease, and others can also be spread by blood product transfusions. But because potential donors are screened with questions about their health status and travel, such cases are very rare.

Other risks

Some look-back studies have suggested patients with certain cancers, like colorectal, prostate, lung (small cell or non-small cell), and breast cancer, had worse outcomes if transfusions were given before or during surgery and/or while getting chemotherapy. The reasons for this were not clear, though it’s possible that transfused blood might affect the immune system in ways that may cause problems later. But it’s also important to know that many of the studies were comparing groups that may have started with major differences between them. For instance, patients who need transfusions are often sicker to start with, and might have had worse outcomes based on that alone. Also, the transfused patients might have been treated in different ways during surgery and afterward.

The American Cancer Society medical and editorial content team
Our team is made up of doctors and master’s-prepared nurses with deep knowledge of cancer care as well as journalists, editors, and translators with extensive experience in medical writing.

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Last Medical Review: June 20, 2016 Last Revised: February 7, 2017

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