Blood-type

blood group.
noun
another name for blood group

blood type
Any of the four main types into which human blood is divided: A, B, AB, and O. Blood types are based on the presence or absence of specific antigens on red blood cells. Also called blood group.

Our Living Language : Blood transfusions used to be the treatment of last resort, since they often caused death. But in the 1890s Austrian scientist Karl Landsteiner began to solve the transfusion puzzle when he found that all human red blood cells belonged to one of four groups which he named A, B, AB, and O. The types refer to antigens found on the surface of these cells. Antibodies circulating in a person’s blood normally recognize the antigens in that same person’s blood cells and don’t react with them. However, if a person with one blood type is transfused with blood of another type, the antibodies bind to the foreign antigens, causing dangerous clumping of the blood. Thus the key to a successful transfusion is to give a person blood that has matching antigens. In the first half of the twentieth century, the study of Rhesus monkeys, which share many biological characteristics with humans, gave rise to the recognition of a human blood protein called the Rh factor. People who have this blood protein are considered Rh positive, while individuals who lack the protein are referred to as Rh negative. The Rh factor is connected to an individual’s blood type. If a person has type AB blood with a positive Rh factor, his or her blood type is referred to as AB positive. The Rh factor causes a problem in a fetus whose blood is Rh positive and whose mother is Rh negative because the mother’s negative blood attacks the positive blood of the fetus. In this instance, a blood transfusion to the fetus can save its life.

Note: Blood transfusions can be given only between donors and recipients who have compatible types; if the types are not compatible, the blood of the recipient forms antibodies against the blood of the donor. There are four basic groupings — A, B, AB, and O — and within these groupings, the Rh factor may be present or absent.