Overview

Your body needs blood to carry the oxygen from the air you breathe into every tissue, and to deliver carbon dioxide and other waste products to the lungs to exhale them. Blood has several components, including red blood cells, white blood cells, platelets, and plasma. Each of these components plays a critical role in helping your body function properly.

Cancer can cause either internal or external bleeding or reduce your body’s ability to make blood cells. Treatments for cancer can also reduce your blood cell counts. To make up for any shortages you might have in a particular blood component, your doctor might order a blood transfusion. In this procedure, a unit of blood (usually containing only the blood component or components you need) from a volunteer donor is slowly dripped through a tube into your vein.

Blood transfusions can cause some minor complications, such as fever and allergic reactions. In very rare cases, they can lead to more dangerous reactions. To minimize the risk of these complications, blood banks have developed many safeguards to make sure that blood is only collected from healthy donors. They test all donated blood to make sure that it cannot pass on a virus or anything else that could make the recipient ill.

Although blood transfusions are generally safe, doctors try to use them only when absolutely necessary in case they lead to a complication. Several techniques are available, including special surgical approaches, to minimize a patient’s need for a blood transfusion.

Human Blood: Its Function and Components

Blood is a liquid that your body uses to carry oxygen from the air you breathe and nutrients from the food you eat throughout your body and to take waste products (such as carbon dioxide) out. Blood also helps your body fight infections and heal wounds. Your heart pumps your blood through your arteries and veins to every cell in your body.

When people donate blood, they usually donate whole blood. Depending on their needs, most of the time people receive the components of blood rather than whole blood. Whole blood contains all of the blood components listed below. Very few people need whole blood transfusions, so after someone donates blood, a technician usually separates the blood into different components. Doctors can then give patients only the components they need.

Your blood has many parts, or components, and each has a different role to play. The components of blood are:

• Red blood cells - When you breathe in, the air goes into your lungs. Red blood cells contain the protein hemoglobin, which lets them carry oxygen from your lungs through your bloodstream and deliver it to every part of your body. They also take carbon dioxide from your tissues to your lungs, so that you can get rid of it by breathing out. The hemoglobin in your red blood cells gives your blood its red color. Hemoglobin is a protein that attaches to oxygen. If you don’t have enough red blood cells, your bloodstream will carry less oxygen throughout your body. This condition is known as anemia. Anemia can make you feel weak, tired, lightheaded, or dizzy.

  Your bone marrow, the soft spongy center of some of your bones, makes all of your red blood cells. Your kidneys keep track of the number of red blood cells in your body. When the kidneys detect that you don’t have enough red blood cells, they release the hormone erythropoietin. Hormones are chemical substances that are formed in one part of the body that affect another part of the body.

  The erythropoietin causes your bone marrow to make more red blood cells. If you need a transfusion of red blood cells, you will probably receive packed red blood cells. This means that a lot of the plasma and other blood cells have been taken out of the blood before you receive it.

• White blood cells - White blood cells, which are also known as leukocytes, help your body fight infection. Like red blood cells, white blood cells are made in your bone marrow. Certain white blood cells called neutrophils and monocytes can move from the blood into the tissues. Once they are in the tissues, these cells ingest, or eat, invading bacteria (organisms that can cause infections and disease) and fungi (plantlike organisms, such as yeasts and molds, that can cause infections), which helps cure the infection.

  If you have very low white blood cell counts and a serious infection, you might receive a transfusion of granulocytes, a type of white blood cell. You might be given granulocytes that have been collected by apheresis, a special process that removes only the granulocytes from the donor’s blood and returns all of the other blood components to the donor’s body. Alternatively, you might be given something called “buffy coat,” which is made up of granulocytes that have been separated from a unit of whole blood.

  Granulocyte transfusions are less common now that artificial colony-stimulating factors and better antibiotics have become available. Granulocyte transfusions can also cause serious side effects.

• Plasma - Plasma is a pale, yellow liquid that does not contain cells but does contain water, proteins, and salts. Some of these proteins are clotting factors, which make your blood clot when you have an injury. Clots help seal your blood vessels when you have a cut and stop your bleeding. Antibodies are other proteins in your plasma that help your body fight infection. If you bleed too much or don’t have enough clotting factors in your blood, you might need a plasma transfusion.

  If you need a plasma transfusion, you will probably receive fresh frozen plasma, which was frozen and stored soon after it was collected from the blood donor. If your levels of clotting factors are low, you might get fresh frozen plasma only, or both fresh frozen plasma and cryoprecipitate.

• Platelets - Your bone marrow makes platelets and your blood carries the platelets throughout your body. These pieces of blood cells help the clotting factors in your plasma stop bleeding. When you are bleeding, your platelets go to the injured spot, clump together, and physically plug the hole to stop the bleeding. If your blood does not have enough platelets, your blood will not clot normally. This low-platelet condition is known as thrombocytopenia.

  A unit of whole blood does not usually have very many platelets. If you need a transfusion of platelets, you might receive a combination of platelets from different donors. However, platelets are sometimes collected by apheresis, a process that removes only the platelets from the blood and returns all of the blood cells and plasma back to the donor’s body. This technique collects enough platelets from one person for a transfusion. If you receive platelets collected by apheresis from just one donor, these are known as “single donor” platelets.

• Cryoprecipitate - Cryoprecipitate contains certain clotting factors. When the technician freezes blood from a donor and thaws it in the refrigerator, a small amount of plasma separates out, or precipitates. This plasma is called cryoprecipitate. It has several of the clotting factors that are usually found in plasma, but it has more of them in the same amount of liquid.

  A unit of whole blood does not have much cryoprecipitate. If you need a cryoprecipitate transfusion, you will probably receive cryoprecipitate from several units of whole blood (from several different donors), as well as fresh frozen plasma. Very few people with cancer need a cryoprecipitate transfusion, unless they are bleeding.