Structure and Functions (Magill’s Medical Guide, Sixth Edition)
Blood replacement in emergency or surgery can be critical: Blood loss exceeding 40 percent can lead to a condition called shock in which the heart cannot pump efficiently, resulting in death. In the search for human blood replacements, scientists have found that animal blood is not compatible. More important, they have discovered that even the blood from different humans does not always mix. Sometimes the red blood cells will agglutinate; that is, they will settle out of the plasma in clumps. Consequently, these red blood cells will be destroyed by the body, and jaundice and death may follow. To prevent this reaction, human blood must be classified into types and cross-matched. The two most important general groupings are the ABO and Rh types.
Human blood is classified into types according to the antigens that might be present on the red blood cells as a result of heredity. Antigens are usually large, complex molecules made of protein alone, protein with attached carbohydrates, or lipids with attached fatty acids and alcohol. They may be free molecules, as in the case of toxins released by invading bacteria, or they may be located on a cell’s surface and serve to label or mark the cell. The markers attached to cell surfaces identify the cell as “self” or “foreign.” Such antigens are the basis of blood types.
Karl Landsteiner was able to show that there are four major blood types, based on two...
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Disorders and Diseases (Magill’s Medical Guide, Sixth Edition)
The discovery of the ABO system allowed transfusions to proceed with some confidence of success during World War I. Still, some transfusions produced problems, and some minor independent blood-type systems (MNS, P) were discovered. Clearly, people were members of more than one blood-type system. The additional discovery of the highly reactive Rh factor or D antigen was critical for safe transfusions.
Another immediate application of the discovery was in the area of childbirth. Rh incompatibility explained why some babies either died at birth or were born in serious trouble. The attack of the mother’s antibodies on the fetal blood cells can lead to various forms of hemolytic disease of newborns, or erythroblastosis fetalis. Incompatibility between mother and child is also one of the causes of spontaneous miscarriage early in pregnancy. Knowing the existence of the Rh factor has saved countless infants.
Recall that the Rh factor is inherited. If an Rh-negative woman (dd) marries an Rh-positive man (DD or Dd), the child may be Rh positive. During pregnancy, there is no direct blood flow from mother to child because red blood cells cannot cross the placenta. At some time during the pregnancy or at birth, however, blood will probably mix, and the mother will then be sensitized. She then will form antibodies against the Rh factor. Many of these antibodies are of the IgG type and are smaller than A or B antibodies...
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Perspective and Prospects (Magill’s Medical Guide, Sixth Edition)
Few successful blood transfusions took place before 1900. In that year, Karl Landsteiner discovered that there were different types of blood. Some would mix, while others would clump. He and his coworkers identified four major human blood groups: A, B, AB, and O. Even so, eight years passed before the first transfusion using Landsteiner’s ABO types was attempted. Transfusions now were more likely to succeed. People could be typed by the antigens on their blood cells, and donors could be matched with the patient. Yet sometimes the transfusions still did not work as predicted. In 1930, Landsteiner won the Nobel Prize in Physiology or Medicine for his discovery of ABO blood types.
Landsteiner and Philip Levine discovered the MNS types in 1927; these are not important in transfusions but are of great help in cases of doubtful paternity. Levine, beginning his own work, had agreed with Landsteiner not to study new blood groups; Landsteiner had reserved that project for himself. Nevertheless, in 1939 Levine and Rufus E. Stetson published a report showing that the blood of a mother with a stillborn child was able to react hemolytically with 80 out of 104 ABO compatible donors. They correctly concluded that the mother’s blood lacked an antigen which many others had: an unknown marker that was independent of the known ABO, MNS, and P blood groups. Levine and Stetson had correctly analyzed the problem but did not name...
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For Further Information: (Magill’s Medical Guide, Sixth Edition)
Bibel, Debra Jan, ed. Milestones in Immunology. New York: Springer, 1988. Offers the reader selections from the original papers of important scientists. The commentary is valuable in understanding the importance of the work. Both Landsteiner and Levine are included.
Jandl, James H. Blood: Textbook of Hematology. 2d ed. Boston: Little, Brown, 1996. Discusses the field of hematology and diseases of the blood. Includes a bibliography and an index.
Martin, Richard J., Avroy A. Fanaroff, and Michele C. Walsh, eds. Fanaroff and Martin’s Neonatal-Perinatal Medicine: Diseases of the Fetus and Infant. 2 vols. 8th ed. Philadelphia: Mosby/Elsevier, 2006. This classic reference work is one of the most comprehensive to date and features discussions on the diverse practice of neonatal-perinatal medicine, pregnancy disorders and their impact on the fetus, delivery room care, provisions for neonatal care, and the development and disorder of organ systems.
Moore, Keith L., and T. V. N. Persaud. The Developing Human. 8th ed. Philadelphia: Saunders/Elsevier, 2008. An outstanding textbook on human embryonic development, with specific information about the causes of congenital malformations and common defects occurring in each of the body’s systems.
Page, Jake. Blood: The River of Life. Washington, D.C.: U.S. News Books, 1981. A beautifully illustrated book about...
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Rh Factor (Encyclopedia of Science)
Rh factor is a protein called an antigen that is found on the red blood cells of most people. (An antigen is any substance that the body considers "foreign" and thus stimulates the body to produce antibodies against it.) Rh factor, like the blood types A, B, and O, is inherited from one's parents. A simple blood test can determine blood type, including the presence of the Rh factor. About 85 percent of white Americans and 95 percent of African Americans have the Rh factor and are known as Rh-positive. Those without the Rh factor are Rh-negative.
Rh factor in pregnancy
Rh factor plays a critical role in some pregnancies. If a woman who is Rh-negative becomes pregnant by a man who is Rh-positive, the fetus may inherit the Rh factor from its father and be Rh-positive. If the blood of the fetus becomes mixed with the mother's Rh-negative blood, a disease called erythroblastosis fetalis can occur in future pregnancies, resulting in destruction of the fetus's red blood cells, brain damage, and even death.
The mixing of blood does not normally occur but may take place before or during birth if a tear in the placenta (the organ through which nutrients pass from the mother to the fetus) allows some fetal blood to enter the mother's circulatory system. If this happens, the fetus's red blood cells bearing the Rh factor stimulate the mother's white blood...
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Rh Factor (Encyclopedia of Nursing & Allied Health)
Rh (Rhesus) factor is a blood protein that plays a critical role in some pregnancies. People without Rh factor are known as Rh negative, while people with the Rh factor are Rh positive. If a woman who is Rh negative is pregnant with a fetus who is Rh positive, her body may make antibodies against the fetus's blood. This can cause Rh disease in the baby, also known as hemolytic disease of the newborn, or erythroblastosis fetalis. In severe cases, Rh disease leads to brain damage and even death. Since 1968 a vaccine has existed to prevent the mother's body from making antibodies against the fetus's blood.
Rh factor is an antigen found on the red blood cells of most people. Rh factor, like the blood types A, B, and O, is inherited from one's parents. A simple blood test can determine blood type, including the presence of the
Rh factor. About 85% of white Americans and 95% of African-Americans are Rh positive. A person's own health is not affected by the presence or absence of Rh factor.
Rh factor is important only during a pregnancy in which an Rh negative woman is carrying a fetus who might be Rh positive. This can occur when an Rh negative woman conceives a baby with an Rh positive man. The gene for Rh positive blood is dominant over the gene for Rh negative blood, so their baby will be Rh positive. If the Rh positive father also carries the gene for Rh negative blood, his babies have a 50% chance of inheriting Rh negative blood and a 50% chance of inheriting Rh positive blood. If both parents are Rh negative, their babies will always be Rh negative. In order to protect their future babies from Rh disease, all women of childbearing age should know their Rh status before becoming pregnant.
Role in human health
Rh factor in pregnancy
The danger of Rh disease begins when the mother's Rh negative blood is exposed to the baby's Rh positive blood. This mixing of blood can occur at the time of birth, and after an abortion or miscarriage. It may also happen during prenatal tests such as amniocentesis and chorionic villus sampling. More rarely, blood from the mother and fetus may mingle during pregnancy, before birth. When this contact occurs, the mother's body responds by building antibodies to fight the foreign Rh blood protein. The mother's blood is now said to be "sensitized" against Rh factor blood.
Common diseases and disorders
Once a mother's blood has become sensitized, her antibodies will attack the blood of any Rh positive fetus that she carries. The antibodies will destroy the fetus's red blood cells. If this happens, the infant will suffer from Rh factor incompatibility. It will become anemic, a condition caused by a reduction in red blood cells and marked by weakness and fatigue. Severe anemia can lead to heart failure and death. The breakdown of red blood cells will also cause the formation of a reddish-yellow substance known as bilirubin. An infant with high levels of bilirubin will look yellowish. This is known as jaundice. Brain damage can occur if the bilirubin level gets high enough. However, Rh incompatibility occurs in varying degrees of severity, with brain damage at the far end of a spectrum.
Rh disease is usually not a problem during a first pregnancy. This is because the Rh negative mother probably will not become sensitized until her blood mixes with the baby's blood during birth. Her baby will be born before her blood can produce antibodies against the baby's Rh positive blood. Once a mother is sensitized, however, any future babies with Rh positive blood will be at risk for Rh disease.
PREVENTION AND TREATMENT. Since 1968 a vaccine has existed to prevent sensitization from occurring. This is the best way to eliminate Rh disease. Available as an injection, the vaccine is called Rh immune globulin (brand name RhoGAM). It blocks the action of the antibodies and prevents the mother's blood from attacking the baby's blood. To be effective, the vaccine must be given any time fetal blood mixes with maternal blood: after birth, abortion, miscarriage, or prenatal tests like amniocentesis and chorionic villus sampling. The vaccine is typically given within 72 hours of any of these events. Since mixing of the blood may also occur during the last three months of pregnancy, the vaccine is also administered at 28 weeks of pregnancy.
A pregnant woman who has already been sensitized from a previous pregnancy will want her doctor to carefully monitor the level of antibodies in her blood throughout her pregnancy. As long as the antibody levels remain relatively low, no problem exists. But if those levels rise, the fetus will need special attention. High antibody levels mean that the fetus's red blood cells are being attacked and destroyed.
A fetus whose red blood cells are being destroyed will need a blood transfusion while it is still in the uterus. Two or three transfusions may be necessary before the baby is born. If the fetus shows signs of illness close to its anticipated birth, the physician may elect to deliver the baby early, either by inducing birth or by cesarean section. The baby will then receive a transfusion after birth.
ELIMINATING RH DISEASE. Until the introduction of the Rh immune globulin vaccine, Rh disease could not be prevented. About 45 babies per 10,000 births developed the disease each year before widespread use of the vaccine in the early 1970s. Use of the Rh immune globulin vaccine has reduced the chances of the mother becoming sensitized from approximately 12-13% to 1-2%.
Nevertheless, the disease is not completely eradicated. Further steps must be taken, since this is a preventable disease. The majority of cases of Rh disease are the result of women not receiving the vaccine at the appropriate time. Poor women without health insurance, who are likely to lack adequate prenatal care, are especially vulnerable to this oversight. Older women may have become sensitized before the vaccine was available; foreign-born women may not have had access to the vaccine.
Amniocentesis procedure in which a sample of the fluid in the amniotic sac is removed with a needle for genetic testing.
Antigen substance, usually a protein or carbohydrate, that stimulates a response from the immune system.
Bilirubineddish-yellow substance formed by the breakdown of red blood cells.
Chorionic villus sampling procedure in which a sample of the membrane surrounding the fetus is taken for genetic testing.
Prenatal testrocedure done to determine the presence of disease or defect in a fetus.
Sensitizationccurs when a mother's blood produces antibodies against the blood of her Rh positive fetus.
Salem, Leon. "Rh incompatibility." eMedicine Journal 2 (May 16, 2001): <<a href="http://www.emedicine.com/emerg/topic507.htm">http://www.emedicine.com/emerg/topic507.htm>.
"Rh Factor and Pregnancy." University of Michigan Health System Website. 1999. July 9, 2001. <<a href="http://www.smartmoms.org/prenatal-tests/test8.html">http://www.smartmoms.org/prenatal-tests/test8.html>.