Blood Transfusion and Donation

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How blood transfusions are done

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. Coagulation (clotting) tests may also be done if abnormal bleeding is a problem.

If a transfusion is needed, 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 (described in the section called “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 (an-tuh-jens) on a person’s blood cells. The 2 most important antigens in blood typing are called A, B, O, and Rh.

Each person is an ABO blood type – either A, B, AB, or O – which means antigen A, antigen B, both antigens, or neither antigen 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 (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 is only used in extreme 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 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 A, Rh-positive blood is called A positive, whereas a person with type A, Rh-negative blood is A 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. If an Rh-negative woman makes antibodies like this, it can 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 do not 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, and blood type

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 (AN-tih-bah-dees) besides those against A, B, and Rh. (Antibodies are made by the body in response to antigens.) 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. Acetaminophen (Tylenol®) and diphenhydramine (Benadryl®) are often given before a transfusion to help reduce the symptoms of minor transfusion reactions.

Red blood cell transfusions are usually started at a slow rate 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. Each unit of red blood cells is usually transfused over a couple of hours, and should be completed within 4 hours. Other components, like plasma and platelets, go in much faster – smaller volumes take much less time.

A visiting nurse can give transfusions in the home if precautions are taken to be sure the patient is kept safe. Patients who get home transfusions are often very sick, not able to travel to a health care facility, and need frequent transfusions for a long time.

The same standards that apply to hospital transfusions must be followed in the home. A doctor must be sure that a patient’s heart and lung function are stable before they can be transfused at home. Emergency medical care must be available close by in case it is needed. Also, the blood must be kept at a certain temperature while being taken to the home.

Last Medical Review: 10/07/2013
Last Revised: 10/07/2013