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Red blood cells (packed RBCs)

Plasma (fresh frozen plasma), once thawed, is transfused to treat bleeding disorders when many clotting factors are missing. This occurs in liver failure, when too much of a blood thinner called Coumadin has been given, or when severe bleeding and massive transfusions result in low levels of clotting factors.

Platelets are transfused in people with low platelet count (thrombocytopenia) or abnormally functioning platelets. Each unit of platelets raises the platelet count by approximately 5,000 platelets per microliter of blood.

Albumin makes up 60 percent of the protein in plasma, is produced in the liver and is used when blood volume needs to be increased and fluids have not worked, as in cases of severe bleeding, liver failure and severe burns.

Immunoglobulins are given to persons who have been exposed to a certain disease such as rabies, tetanus or hepatitis to help prevent that disease.

Factor VIII concentrate and cryoprecipitate are used in hemophilia A (classic hemophilia) since this is caused by a factor VIII deficiency.

Factor IX concentrate is used in hemophilia B ("Christmas disease"), which is caused by a deficiency of clotting factor IX.

Ensuring a Safe Blood Supply

There are many tests that are performed on blood to ensure its safety. These tests include checking for:

Hepatitis B surface antigen
Hepatitis B core antibody
Hepatitis C antibody
HIV-1, HIV-2 antibodies
HIV-1 p24 antigen
HTLV-1, HTLV-2 antibodies

If any of these tests are positive, the blood is discarded. As of 1996, the risk of getting HIV from a single blood transfusion was 1 in 676,000 units of blood, the risk of developing Hepatitis B was 1 in 66,000 units and the risk of getting Hepatitis C was 1 in 100,000 units. However, newer testing may decrease the risk of Hepatitis C to between 1 in 500,000 and 1 in 1,000,000.

When blood is transfused into a patient, the blood type must be determined so that a transfusion reaction does not occur.

A reaction occurs when the antigens on the RBCs of the donor blood react with the antibodies present in the recipient's plasma. In other words, if donor blood of type A (contains A antigens) is given to someone with type B blood (they have anti-type A antibodies in their blood), then a transfusion reaction will occur.

The opposite does not occur. It is unusual for the antibodies in the plasma of the donated blood to react to the antigens on the recipients RBCs because very little plasma is transfused and it gets diluted to a level too low to cause a reaction.

When a transfusion reaction occurs, an antibody attaches to antigens on several RBCs. This causes them to clump together and plug up blood vessels. Then they are destroyed by the body (called hemolysis ), releasing hemoglobin from the RBCs into the blood. Hemoglobin is broken down into bilirubin, which can cause jaundice . These events occur in hemolytic disease of the newborn (mentioned previously).

When an emergency blood transfusion is necessary and the recipient's blood type is unknown, anyone can get type O- blood transfused since type O- blood has no antigen on its surface that could react with antibodies in the recipient's plasma. Therefore, someone with type O- blood is called a universal donor . Someone with type AB blood is called a universal recipient because they have no antibodies that could react with donated blood.

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