22.26
Grupo sanguíneo Rh
O antígeno Rh (Rh) é crucial para determinar os grupos sanguíneos e garantir a compatibilidade durante as transfusões de sangue.
O antígeno Rhesus e o…
O antígeno Rh ou Rh é uma classe de aglutinogênio nos glóbulos vermelhos ou hemácias. Sua presença ou ausência categoriza uma pessoa como Rh-positiva ou Rh-negativa.
Ao relatar o grupo sanguíneo de uma pessoa, o antígeno Rh é normalmente combinado com os antígenos A e B.
Por exemplo, o tipo sanguíneo de uma pessoa com antígenos A e Rh é designado como A-positivo. Por outro lado, na ausência do antígeno Rh, o sangue da pessoa é referido como A-negativo.
Ao contrário do sistema ABO, o plasma não contém naturalmente anticorpos anti-Rh.
Assim, a exposição ao antígeno Rh pode desencadear uma resposta imune em indivíduos Rh-negativos, levando à hemólise.
Por exemplo, suponha que uma mãe Rh negativa carregue um feto Rh positivo. Nesse caso, o sistema imunológico da mãe reconhece o antígeno Rh nas hemácias fetais como estranho, desencadeando a produção de anticorpos anti-Rh.
Normalmente, esses anticorpos não interferem na primeira gravidez. No entanto, em gestações subsequentes com fetos Rh-positivos, as hemácias fetais correm risco de hemólise devido aos anticorpos anti-Rh existentes no sangue da mãe.
View the full transcript and gain access to JoVE Core videos
Q1: What is the Rh antigen and how does it determine blood type?
The Rh antigen is a protein on red blood cell surfaces that classifies blood as Rh-positive or Rh-negative. Its presence or absence is combined with ABO antigens to designate complete blood types, such as A-positive or B-negative. Understanding the Rh factor is essential in transfusion medicine for ensuring blood compatibility.
Q2: Why don't Rh-negative people naturally have anti-Rh antibodies?
Unlike the ABO system, plasma does not naturally contain anti-Rh antibodies. Anti-Rh antibodies develop only after exposure to the Rh antigen, triggering an immune response in Rh-negative individuals. This delayed response is why first transfusions with incompatible Rh blood may not cause immediate problems, but subsequent exposures carry greater risk.
Q3: How does Rh incompatibility affect pregnancy and the fetus?
When an Rh-negative mother carries an Rh-positive fetus, her immune system may recognize fetal Rh antigens as foreign, producing anti-Rh antibodies. In the first pregnancy, these antibodies typically cause no harm. However, in subsequent pregnancies with Rh-positive fetuses, existing antibodies cross the placenta and attack fetal red blood cells, causing hemolysis and hemolytic disease of the newborn.
Q4: What is RhoGAM and how does it prevent hemolytic disease of the newborn?
RhoGAM is a serum containing anti-Rh antibodies administered to Rh-negative mothers during and after delivery of Rh-positive babies. It prevents the mother's immune system from recognizing fetal Rh antigens as foreign, stopping anti-Rh antibody production. This protective measure significantly reduces the risk of hemolytic disease in future pregnancies.
Q5: How is the Rh blood group reported alongside the ABO system?
The Rh antigen status is combined with ABO antigens when reporting blood type. A person with A and Rh antigens is designated A-positive, while someone with A antigens but no Rh antigen is A-negative. This combined classification ensures accurate blood matching for transfusions and identifies potential maternal-fetal incompatibility risks.
Q6: What happens when Rh-negative individuals receive Rh-positive blood?
Exposure to Rh-positive blood triggers an immune response in Rh-negative individuals, leading to anti-Rh antibody production. This can cause hemolysis, the destruction of red blood cells, resulting in transfusion complications. Subsequent transfusions with Rh-positive blood carry increased risk of severe hemolytic reactions due to existing antibodies.
Q7: Why is understanding Rh compatibility critical in transfusion medicine?
Incompatible Rh factors between donor and recipient trigger immune responses causing hemolysis and potential life-threatening complications. Proper Rh typing prevents transfusion reactions and is especially vital for Rh-negative recipients who lack natural anti-Rh antibodies. Accurate Rh classification ensures safe blood matching and protects patient health during transfusions.