Rh factor is a substance on the red blood cells of most people. Red blood cells that contain the Rh factor agglutinate (clump) if they come into contact with an antibody called anti-Rh. This reaction can produce serious illness or death. People who have the Rh factor are known as Rh-positive. Those lacking it are Rh-negative. Karl Landsteiner, Philip Levine, and Alexander Wiener discovered the factor in rhesus monkeys in 1940. They named it Rh for the monkey.
Anti-Rh does not occur naturally in the blood. But if an Rh-negative person receives a transfusion of Rh-positive blood, anti-Rh may build up in the blood plasma. By the time the antibody has been produced, the donor blood usually is so diluted that no serious reactions take place. But if the patient receives later transfusions of Rh-positive blood, the anti-Rh will attack the Rh-positive red blood cells and cause agglutination.
The Rh factor is inherited. The child of an Rh-negative mother and an Rh-positive father may be Rh-positive. Before birth, some of the baby’s blood cells may enter the mother’s blood. Then the mother may build up anti-Rh. Most of the antibody does not form until after the baby is born, however, so it seldom causes any problems with the first child. But if the mother becomes pregnant with another Rh-positive baby, she now has a ready-made supply of anti-Rh. The flow of large amounts of her anti-Rh into the child’s blood can cause clumping and destruction of the infant’s red blood cells. This condition, which is called erythroblastosis fetalis, can result in severe anemia, brain damage, and even death. Such severe reactions take place in only about 1 of 20 cases in which the mother is Rh-negative and the father is Rh-positive. Even among these couples, physicians can usually prevent erythroblastosis fetalis by injecting the mother with a serum shortly after she gives birth to an Rh-positive child. The serum contains anti-Rh, which destroys any of the baby’s cells in her blood before her body has time to produce its own anti-Rh. When erythroblastosis fetalis does occur, doctors treat the condition by replacing the baby’s blood with fresh blood. In most cases, this procedure eliminates any long-term effects of the disease.
