A doctor may prescribe a transfusion for a cancer patient if he or she is having symptoms that may be related to low blood cell levels. First, lab 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. These tests measure 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 involved.

Blood types

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 most important groups of antigens in blood typing are called ABO and Rh. Each person has 1 of 4 possible ABO types (A, B, AB, or O) and 1 of 2 possible Rh types (Rh-positive or Rh-negative). These 2 factors can be combined into 8 possible blood types.

Blood types are important when it comes to transfusions. If you receive a blood component transfusion that is not compatible with your blood type, your body's immune system could mount a defense against the donated blood. This can cause a serious or even life-threatening transfusion reaction (described below in the section, "Possible risks of blood product transfusion").

To be sure no mistakes are made, donated blood is carefully "typed" (tested to find out what type it is) both when it is taken from the donor and again once it is received by the hospital lab. The blood bag is labeled with the type of blood inside it. When a person needs a blood transfusion, a blood sample is drawn from him or her and tested the same way.

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 (about 45% of the population), followed closely by type A.

If you have type "O" blood, you have neither A nor B antigens on your red blood cells, and your plasma has antibodies (immune system proteins) against both A and B antigens. You can only get type O red blood cell transfusions. But your red blood cells could be given to people with type A, B, AB, or O blood, which is why you are sometimes called a "universal donor." It is only in extreme emergencies that universal donor blood is used in this way. For example, if a person is bleeding severely and nearing death, there may no time for testing. In everyday practice, people are always given the exact same blood type that they have.

If you have type "A" blood, you have the A antigen on your red blood cells. Since you do not have B antigen on your cells, your body makes antibodies against the B antigen. These antibodies are in your plasma and prevent you from getting either type B or AB red blood cells.

If you have a "B" blood type, you have the B antigen on your red blood cells and have antibodies against the A antigen in your plasma.

If you are an "AB" blood type, you have both the A and B antigens on your red blood cells and do not have antibodies against either of these antigens in your plasma.

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 that has type A, Rh-positive blood is called "A positive," whereas a person with type A, Rh-negative blood would be "A negative."

If you have Rh-positive blood, you can receive 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 emergencies. Rh-positive blood 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 cause harm to 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, but these are rare because people do not make antibodies against them unless they have had a transfusion before.

Plasma transfusions follow a different set of rules (based on the antibodies in the plasma):

• People with type O blood can receive any type of plasma.

• People with type A blood can receive A or AB plasma.

• People with type B blood can receive B or AB plasma.

• People with type AB blood can receive only AB plasma.

• The Rh type is usually not a factor in plasma transfusions.

For platelet and cryoprecipitate transfusions, matching the blood type of the donor to the recipient is usually not critical, but labs usually do try to match them if possible. It may become important in patients who have already had many transfusions or who have had transfusion reactions in the past.

Crossmatching

Before a person can get a transfusion of packed red blood cells, a lab test called a cross-match must be done to make sure that the donor blood is compatible with (matches) the recipient. A unit of the proper ABO and Rh type is selected, and a drop of donor blood is mixed with a drop of plasma from the patient. If no problems are encountered, a cross-match takes about 30 minutes. Another test called an antibody screen is done to see if a patient's plasma contains antibodies other than ABO and Rh. If this is the case, some units of donor blood may not match the recipient's, even though they have the same ABO and Rh types.

A cross-match is usually not necessary for a platelet or plasma transfusion unless the platelets appear to contain some red blood cells.

Getting a transfusion

Most blood transfusions are given in the hospital or in outpatient clinics. The medicines acetaminophen (Tylenol) and diphenhydramine (Benadryl) are often given before a transfusion to help prevent transfusion reactions. Blood or blood products are infused through a vein, usually in the arm. The patient is watched closely for the signs and symptoms of a transfusion reaction, and vital signs (such as temperature, heart rate, and blood pressure) are checked often. Each unit of blood or blood product is usually transfused over a couple of hours, although smaller volumes of platelets may take less time.

Receiving blood transfusions at home: A visiting nurse can give blood transfusions in the home if precautions are taken to be sure the patient is kept safe. Patients who receive home blood transfusions often have severe chronic illnesses, are 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 if needed. Also, care must be taken to make sure the blood is kept at the proper temperature while being taken to the home.

Revised: 03/08/2008