ABO: The most important of several blood group systems for typing human blood, based on the presence or absence of two antigens (A and B) on the surface of red blood cells. Blood types are A, B, AB, and O.

Allogeneic: Transfusion of blood from a person other than the recipient, (i.e., NOT autologous). Same as homologous.

Anemia: Condition in which the red cell content of the blood is below normal limits. Most common cause is a deficiency of iron, an element necessary for the formation of hemoglobin.

Antibody: A protein produced by the immune system in response to a specific foreign substance (antigen) that attempts to eliminate the foreign substance from the body.

Antigen: A protein or carbohydrate substance that is recognized by the body as foreign that stimulates an immune response.

Apheresis: An automated method of separating platelets, plasma, or red blood cellsfrom the donor's blood and returning all but that component to the donor. Also known as Apheresis Blood Collection, or ABC.

Autologous Donation: From auto (self) and logos (relation), it is a blood donation you give for your own surgery or medical needs.

Bone Marrow: The site of blood cell production, found within bone cavities.

Cholesterol: Complex chemical present in all animal fats and widespread in the body and nerve fiber sheaths.

Cryoprecipitate: Component of blood obtained by freezing and thawing plasma. Useful in replacing some clotting factors in patients missing them congenitally or because of operation or trauma.

Cytomegalovirus (CMV): About half of all donors have antibodies to this virus. Although the virus does not cause significant illness in healthy individuals, CMV may cause severe infection in transplant recipients and other patients whose immune systems are impaired. Other patients can safely receive blood that has this antibody.

Directed Donation: A blood donation for a specific person. The patient's physician must give the order for donation.

Erythrocytes: Red blood cells.

Hematocrit: Measure of the volume of red blood cells as a percentage of the total blood volume. Normal in males is 43-49%, in females 37-43%.

Hemoglobin: An iron-containing protein pigment occurring in the red blood cells and functioning primarily in the transport of oxygen from the lungs to the body tissues.

Hepatitis: Inflammation of the liver.

Homologous: Transfusion of blood from a person other than the recipient (i.e., NOT autologous). Same as allogeneic.

Leukocytes: White blood cells.

Leukoreduced: Blood in which white cells have been reduced in number, usually by filtration.

Plasma: The yellow fluid portion of the blood in which the red cells, white cells, and platelets are suspended. Like other blood components, it can be separated out from the whole blood for use in component therapy. Plasma contains many clotting proteins.

Platelets: Disk-shaped structures found in the blood of all mammals, playing a major role in the coagulation of blood. Patients undergoing treatment for cancer are the primary users of platelets.

Rh factor: An antigen present on the red blood cells of about 85% of people. Called Rh because it was first identified in the blood of rhesus monkeys. Persons with the factor are designated Rh-positive, those lacking the factor are designated Rh-negative.