During a blood transfusion, you receive blood or parts of blood through an I.V. (intravenous) line. The blood may be from a donor. Or you may receive your own blood that has been stored for you. There are several parts of blood that can be transfused. Red blood cells are the most common type of blood product transfusion.

There are many reasons you may need a transfusion. Your doctorr will explain the reasons for your transfusion.

There are several reasons why you may need a blood transfusion, such as:

• A sudden loss of blood due to an accident or injury
• Blood loss as a result of surgery
• A low hemoglobin level before, during, or after surgery (hemoglobin is the protein in red blood cells that carries oxygen)
• Severe heart, lung, liver, or kidney disease
• Bone marrow failure
• Moderate to severe anemia (decreased red blood cells)

Human blood is made of blood cells and a fluid called plasma. Plasma carries red and white blood cells and platelets. Each part of blood has a special function. These parts can be separated from each other. Bone marrow, the soft, spongy material in the center of the bones, makes most of the body's blood cells. Here is a look at each part of the blood, and why it might be transfused:

Red blood cells. These cells carry oxygen from your lungs to other body organs. They also carry carbon dioxide back to the lungs to be breathed out (exhaled). The body needs a certain number of these cells to work well. Bleeding due to injury, surgery, or disease may cause a low red blood cell count. This is the most common type of transfusion.

White blood cells. These cells fight infections by destroying bacteria, viruses, and other germs. White blood cells are rarely transfused. They are often set aside as a short-term (temporary) treatment for people with a low white cell count and severe infection that has not responded to antibiotics.

Platelets. These tiny cells in your blood help form clots and stop bleeding. Your body may not make enough platelets. This might be from bone marrow disorders, increased destruction of platelets, or medicines, such as chemotherapy. Platelets may be transfused before surgery. Or any time the platelet count is very low and you are at risk of bleeding.

Plasma. This fluid carries the blood cells all over the body. It contains proteins, vitamins, and minerals. Some of the proteins also help blood to clot. Plasma or fresh frozen plasma can be transfused in people who severely lack certain parts of the blood that help with clotting.

Most hospitals use blood from volunteer donors. These donors are not paid for giving blood or blood products. Each blood donor must answer medical history questions and have a limited physical exam before being accepted as a donor. Donated blood is carefully tested, which lowers the chances of transfusion-related infections. Donated blood is tested for:

• Hepatitis viruses B and C
• HIV
• Human T-lymphotropic viruses (HTLV) I and II
• Syphilis
• West Nile virus
• Chagas disease, caused by a parasite

Most transfusions are done without any problems. Mild side effects can often be treated with medicine if you need more transfusions. Mild side effects may include symptoms of an allergic reaction, such as:

• Headache
• Fever
• Itching
• Takes more effort to breathe
• Rash

Serious side effects are rare. They may include:

• Trouble breathing
• Chest pain
• Sudden drop in blood pressure

In addition to general volunteer blood donations, there are two other types of blood donation:

Directed blood donation. This is when friends or family donate blood for a certain person. This blood is set aside for that person's use. This type of donation requires a prescription and must be scheduled in advance. Direct blood donations go through the same testing as other volunteer donations. If the person does not use this donated blood, it may be made available for someone else.

Donating blood for yourself (autologous donation). This is your blood that you donate for your own use. It's set aside and can be transfused back into your own body if needed for a later, planned surgery. This type of donation requires a prescription from your doctor and is scheduled in advance. It does not go through the same testing as other blood donations. If you don't use the blood, it's thrown away.

No special preparation is needed before a blood transfusion.

A blood transfusion may occur as part of your hospitalization. Or it may be done as an outpatient. This means you go home the same day.

• Blood is collected and stored in germ-free (sterile) bags. The bags are used once and then thrown away.
• Before blood is given to you, it's cross-matched with your own blood to make sure it's compatible.
• The blood will be given through an I.V. placed in a vein.
• Your temperature, blood pressure, and heart rate will be checked many times while the blood is being given.
• It may take a few hours to complete the process.

• After you have received the blood as requested by your doctor, the I.V. that was placed in your arm will be removed and you will be discharged.
• You will be able to go back to your normal activities, unless your doctor has made other recommendations.

Before you agree to the test or procedure, make sure you know:

• The name of the test or procedure
• The reason you are having the test or procedure
• What results to expect and what they mean
• The risks and benefits of the test or procedure
• What the possible side effects or complications are
• When and where you are to have the test or procedure
• Who will do the test or procedure and what that person's qualifications are
• What would happen if you did not have the test or procedure
• Any alternative tests or procedures to think about
• When and how will you get the results
• Who to call after the test or procedure if you have questions or problems
• How much will you have to pay for the test or procedure