The rhesus factor, or Rh factor, is a protein that may be present on the surface of red blood cells (RBCs). If RBCs contain the Rh antigen, they are Rh-positive, and if not, they are Rh-negative. It is important to know a person’s Rh factor to ensure that they receive compatible blood. Show Blood typing is a system of classifying blood based on the antigens present on or missing from the surface of RBCs. This approach to grouping bloods can prevent the severe complications that can occur from interactions between incompatible blood types. In this article, we discuss the importance of the Rh factor and blood typing. We also explain how a person can determine their Rh status.
The Rh factor is an inherited protein that can be present on the surface of RBCs. There are five main Rh antigens on RBCs, of which the most important is the Rh D antigen. The Rh D antigen is the most immunogenic, meaning that it may provoke an immune response. People inherit their Rh status from their parents, separate from their ABO blood type. Although Rh status can vary among populations, roughly 85% of people in the United States are Rh-positive. RBCs contain proteins, or antigens, on their surface that allow specialists to determine blood types. The absence or presence of A or B antigens and Rh factor can help classify blood types. People with no A or B antigens on the surface of their RBCs have blood type O. Combining these systems creates the eight most common blood types:
The positive or negative sign next to the ABO grouping refers to the Rh status and whether the RhD antigen is present or not. While being Rh-positive is more common, being Rh-negative does not indicate illness, and it does not usually affect a person’s health. However, it can influence their compatibility with other blood types, affecting the type of blood they can receive. Blood typing refers to categorizing blood based on the antigens that are present on the surface of RBCs. In addition to the Rh factor, people can also use the ABO system to determine blood type. However, the 30 known blood groups comprise more than 600 antigenic structures, meaning that some people may have rare blood types. Determining blood types is essential for compatibility. If the immune system detects the antigens in incompatible blood, it will recognize those RBCs as foreign and destroy them, which could result in life threatening complications. Learn more about blood types. The Rh factor is one of the antigens that specialists use to determine blood compatibility. Checking for blood compatibility is a routine procedure during pregnancy, blood transfusions, and blood donation. If a person experiences Rh incompatibility during pregnancy — for example, if they are Rh-negative, and the baby is Rh-positive — they may produce anti-D antibodies. This can cause complications with future pregnancies. Additionally, the Rh factor is important in blood donations and transfusions. For example, an Rh-negative person can only receive Rh-negative blood. Otherwise, they may experience a hemolytic transfusion reaction, which can cause serious complications. The main complication relating to Rh factors involves those who are Rh-negative encountering Rh-positive blood and producing anti-D antibodies in response. This may occur during pregnancy or if a person accidentally receives incompatible blood during a transfusion. When a person who is Rh-negative is pregnant with an Rh-positive fetus, their body will recognize the Rh-positive blood as foreign and produce anti-D antibodies. These antibodies can cross the placenta and attack the fetus’s blood cells. Some people may refer to this as Rh disease. Health problems do not usually occur during an Rh-negative person’s first pregnancy with an Rh-positive fetus, as the body is unlikely to produce enough anti-D antibodies. However, without treatment, later pregnancies may be at risk. An attack by the anti-D antibodies on the fetal blood cells can result in hemolytic disease of the newborn. When RBCs break down, they release bilirubin, which may cause jaundice. Due to a lower number of RBCs, the fetus may also experience anemia and the enlarging of their organs. In severe cases, this may result in a stillbirth. Similarly, Rh-negative people who receive an Rh-positive blood transfusion may experience an incompatible transfusion reaction, known as an acute hemolytic transfusion reaction. This reaction can produce a number of symptoms and rapidly progress to shock. If a person is unaware of their Rh status, a healthcare provider can perform an Rh screening test. This procedure uses a blood sample to determine whether RBCs have the Rh antigen. It is also possible to perform a prenatal test to determine the Rh status of a fetus during pregnancy. People may consider undergoing an Rh screening test if they plan to become pregnant, require a blood transfusion, or donate blood. Every blood donation will undergo an Rh factor screening test, as well as tests for various infectious diseases, to ensure that it is safe for the recipient. Learn more about donating blood. The Rh factor is an antigen that some people may have on their red blood cells. Those who have this antigen are Rh-positive, while those without it are Rh-negative. Knowing a person’s Rh status is key to understanding their blood compatibility. This compatibility is particularly important during pregnancy and when receiving a blood transfusion. In the event of incompatible blood, the body will respond by producing antibodies against the Rh antigen. These antibodies will destroy red blood cells with the Rh antigen, which can cause health complications. Rh factor testing likely wasn’t on your radar before you had a baby on the way. But part of having a healthy pregnancy means getting screened. The Rh factor is a protein carried by red blood cells in some people and not in others. If you don’t have it, you may need a simple but effective treatment during pregnancy to protect you and your baby. Here’s what you need to know about Rh factor testing, how the test works and what it means for your pregnancy if you’re Rh negative. What does Rh factor mean?Rh factor is a type of protein often found on red blood cells, which carry oxygen throughout the body. But not everyone has it. If you carry the protein, you’re Rh positive. If you don’t, you’re Rh negative. Not many people are Rh negative. Negative Rh factor occurs in around 15 percent of white people and between 4 and 8 percent of Black people. In Asian people, the chances of being Rh negative are only around 0.3 percent. Whether you’re Rh positive or negative doesn’t matter much, except when it comes to pregnancy. What is Rh incompatibility?Rh incompatibility is when a mom is Rh negative and her baby is Rh positive, which can cause problems during pregnancy. If the baby’s Rh positive blood cells enter the mother's circulation, her immune system may view them as "foreign" — and, in a normal immune response, mobilize armies of antibodies to attack these unfamiliar cells. Since red blood cells carry oxygen, this type of attack can make it hard for a baby to get the amount of oxygen she needs. That can potentially cause a serious type of anemia and other health problems. It may sound scary, but Rh incompatibility only becomes a problem if you and your baby’s blood mix, most likely during birth. At that point, the antibodies your body makes cannot harm your baby. But they could be dangerous later on if you become pregnant with another Rh positive baby. Why is Rh factor testing important during pregnancy?Having Rh incompatibility can set the stage for problems, particularly if you’re planning on having more children later on. That’s why it’s so important to get tested and, if needed, treat the problem. Fortunately, finding out your Rh status is as easy as taking a blood test. Rh factor screening is typically part of the initial prenatal blood workup. And if you turn out to be Rh negative, the problem is easy to treat. What happens if you test Rh positive?If you test Rh positive, as most of the population is, the issue of compatibility is moot. Whether the fetus is Rh positive or Rh negative, there are no foreign antigens on fetal red blood cells to cause your immune system to mobilize against them. What happens if you test Rh negative?If you test Rh negative, your baby's father will be tested to determine whether he's Rh positive or negative. If he turns out to be Rh negative, your fetus will be Rh negative too. That’s because two Rh negative parents can't have an Rh positive baby. If your baby’s father is Rh positive, however, there's a significant possibility that your fetus will inherit the Rh factor from him, creating an incompatibility between you and your baby. This incompatibility is usually not a problem in a first pregnancy because you don’t have antibodies to the baby's Rh factor yet. However, once a mom's natural protective immune response kicks in and produces antibodies during her first pregnancy or delivery (or abortion or miscarriage), they stay in her system. That becomes a concern if she becomes pregnant again with another Rh positive baby. During the subsequent pregnancy, these antibodies could potentially cross the placenta into the baby's circulation and attack the fetal red blood cells, causing very mild (if maternal antibody levels are low) to very serious (if they are high) anemia in the fetus. Rh incompatibility treatment (RhoGAM)Preventing this antibody response in Mom is the key to protecting the fetus when there is Rh incompatibility. Most practitioners use a two-pronged strategy. If you're Rh negative at 28 weeks, you'll get an injection of Rho(D) immune globulin (RhoGAM) to prevent antibodies from forming. Another dose is administered within 72 hours after delivery if blood tests show your baby is Rh positive. (If your baby is Rh negative, no treatment is required.) The RhoGAM injection should also be administered after any genetic testing that could result in mixing of maternal and fetal blood, such as chorionic villus sampling (CVS) or amniocentesis. Vaginal bleeding or trauma during pregnancy, miscarriage, ectopic pregnancy and abortion are the other situations where fetal blood can get into a pregnant woman's bloodstream, so a RhoGAM injection is given then as well. Getting a RhoGAM shot at these times can head off problems in future pregnancies. If you're Rh negative, did not get a RhoGAM injection during your previous pregnancy, and you've developed antibodies capable of attacking an Rh positive fetus, amniocentesis or a noninvasive blood test can be used to check the blood type of the fetus (though not all insurance will cover the blood test, since it's pricey). If the fetus is Rh positive, and thus incompatible with your blood type, ultrasound tests will be done every week or two to assess the baby's condition. If at any point anemia has developed, a transfusion of Rh negative blood to the fetus may be necessary. This is done through a small needle placed in the umbilical cord under ultrasound guidance. Such transfusions are very effective and associated with excellent outcomes. Thinking about all this can make you anxious if you and your baby are Rh incompatible. The good news is that once the incompatibility is treated, the chances of having a healthy pregnancy and baby are very, very high. In fact, RhoGAM has reduced the need for transfusions in Rh incompatible pregnancies to less than 1 percent. Other blood type incompatibilitiesA similar incompatibility can arise with other factors in the blood, such as the Kell antigen, though these are less common than Rh incompatibility. If the father has the antigen and the mother does not, there's again the potential for problems. Part of the first routine blood test looks for the presence of circulating antibodies in the mom's blood. If these antibodies are found, the father of the baby is tested to see if he's positive, in which case the management is the same as with Rh incompatibility. Rh factor incompatibilities during pregnancy aren’t all that common. But when they do occur, they’re easy to find and treat — so you, your baby and any future children you might have can be protected. |
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