Most blood donations are divided (fractionated) into their components: red blood cells, platelets, clotting factors, plasma, antibodies (immunoglobulins), and white blood cells. Depending on the situation, people may receive only the cells from blood, only the clotting factors from blood, or some other blood component. Transfusing only selected blood components allows the treatment to be specific, reduces the risks of side effects, and can efficiently use the different components from a single unit of blood to treat several people.
Red Blood Cells:
Packed red blood cells, the most commonly transfused blood component, can restore the blood's oxygen-carrying capacity. This component may be given to a person who is bleeding or who has severe anemia. The red blood cells are separated from the fluid component of the blood (plasma) and from the other cellular and cell-like components. This step concentrates the red blood cells so that they occupy less space, thus the term “packed.” Red blood cells can be refrigerated for up to 42 days. In special circumstances—for instance, to preserve a rare type of blood—red blood cells can be frozen for up to 10 years.
Platelets can help restore the blood's clotting ability. They are usually given to people with too few platelets (thrombocytopenia), which may result in severe and spontaneous bleeding. Platelets can be stored for only 5 to 7 days.
Blood Clotting Factors:
Blood clotting factors are proteins found in blood plasma that normally work with platelets to help the blood clot. Clotting factors may be obtained from plasma or manufactured. Manufactured proteins are called recombinant factor concentrates. Without clotting factors, bleeding would not stop after an injury. Individual concentrated blood clotting factors can be given to people who have an inherited bleeding disorder, such as hemophilia or von Willebrand's disease, and to those who are unable to produce enough clotting factors (usually because of severe infection or liver disease).
Plasma, the fluid component of the blood, contains many proteins, including blood clotting factors. Plasma is used for bleeding disorders in which the missing clotting factor is unknown or when the specific clotting factor is not available. Plasma also is used when bleeding is caused by insufficient production of all or many of the different clotting factors, as a result of liver failure or severe infection. Plasma that is frozen right after it is separated from the cells of donor blood (fresh frozen plasma) can be stored for up to 1 year.
Antibodies (immunoglobulins), the disease-fighting components of blood, are sometimes given to provide temporary immunity to people who have been exposed to an infectious disease or who have low antibody levels. Infections for which antibodies are available include chickenpox, hepatitis, rabies, and tetanus. Antibodies are produced from treated plasma donations.
White Blood Cells:
White blood cells are transfused to treat life-threatening infections in people who have a greatly reduced number of white blood cells or whose white blood cells are functioning abnormally. The use of white blood cell transfusions is rare, because improved antibiotics and the use of cytokine growth factors have greatly reduced the need for such transfusions. White blood cells are obtained by hemapheresis and can be stored for up to 24 hours.
Blood substitutes that use certain chemicals or specially treated solutions of hemoglobin (a protein that allows red blood cells to carry oxygen) to carry and deliver oxygen to tissues are being developed. These solutions can be stored at room temperature for up to 2 years, making them attractive for transport to the site of trauma or to the battlefield. However, further research is needed before these blood substitutes become available for routine use.
Last full review/revision July 2007 by Harold S. Kaplan, MD; Donna L. Skerrett, MD