An antigen in red blood cells, which is an element in blood grouping.
A group of antigens that may or may not be present on the surface of the red blood cells; it forms the basis of the rhesus blood group system. Most people have the rhesus factor, i.e. they are Rh-positive. People who lack the factor are termed Rh-negative. Incompatibility between Rh-positive and Rh-negative blood is an important cause of blood transfusion reactions and hemolytic disease of the newborn.
An attribute on the red blood cells of the rhesus monkey which has been found to occur on the red blood cells of certain humans. When it does occur, the person is Rh positive (RH+), when it is absent, the person is Rh negative. This factor provided one of the earliest tests for blood grouping.
A substance discovered in 1940 to be present in the blood of 86 percent of human beings; so named because it was first found in the blood of Rhesus monkeys. The terms Rhesus positive and Rhesus negative are applied, respectively, to blood that possesses or lacks this factor, and Rhesus is commonly abbreviated to Rh. The presence of the Rh factor in the blood of an unborn child of an Rh-negative mother and an Rh-positive father irritates the mother’s blood to produce antibodies against the Rh factor in the baby’s blood. The antibodies then cross the placental barrier and immediately being to dissolve the red blood cells of the fetus. This may result in the baby being born with a blood disorder known as hemolytic disease of the newborn with jaundice. Unless this blood is drained off and replaced by other blood within 48 hours of birth, there is a risk of brain damage resulting in mental retardation. This does not always occur, for the first and usually the second baby of such parents are not affected—it is in the third and fourth pregnancies that trouble arises. Approximately 17 women in every 100 are Rh negative and of these 17, three have Rh-negative husbands. Of the 14 with Rh-positive husbands only about seven will have a Rh-positive baby, so that in every 100 pregnancies there are, on the average, only ten in which the mother is Rh-negative and the baby Rh-positive. Only a few of these babies will have hemolytic disease of the newborn. Routine prenatal care involves determining the mother’s Rh classification. If it is Rh-negative the father’s blood is also tested, and if this is also Rh-negative there is no problem. If, however, the father’s blood is Rh-positive, the mother’s blood is tested at intervals during pregnancy to check whether she is manufacturing Rh antibodies. Should this occur, towards the end of pregnancy, arrangements are made to change the baby’s blood at birth. However, it does not automatically follow that because the mother’s blood contains Rh antibodies her baby will necessarily suffer from hemolytic jaundice. Also called Rh factor.