Blood Group

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    • Blood Groups
      • More than 630 distinct antigens are expressed on the surface of RBCs; how- ever, only a few cause significant problems.
      • ABO antigens
        • The A and B codominant genes code for glycoproteins
        • A and B antigens, are added to an H precursor.(MCQ)
        • Patients homozygous for the O gene produce
          • neither the A nor the B antigen
          • produce only the H precursor.
          • Anti-A or anti-B antibodies are produced to the ABO antigen not expressed by the host.
        • When blood products are required emergently, type O RBCs and type AB plasma may be given with the least concern for transfusion reaction .(MCQ)
      • The Rh (Rhesus) antigens
        • large class of more than 50 related antigens, including D, C, c, E, and e.
        • Rh-positive individuals produce the D antigen
        • Rh-negative individuals
          • do not produce the antigen
          • do not produce antibodies to D unless exposed to it through pregnancy or another form of transfusion. (MCQ)
        • Rh antibodies may induce hemolytic reactions.

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      • Erythroblastosis Fetalis (Hemolytic Disease of the Newborn)
        • It results from incompatibility between fetal and maternal blood groups, most commonly involving the Rh system (D antigen).
        • Sensitization of the mother is required.
        • Blood from Rh-positive fetus passes into the circulation of Rh-negative mother (>1 mL required). (MCQ)
        • Passage is usually transplacental during labor.
        • This leads to the formation of maternal anti-Rh IgM antibodies, which cannot cross the placenta.
        • The maternal immune response matures and IgG antibodies are formed, which can cross the placenta in subsequent pregnancies. (MCQ)
        • The resulting hemolysis varies in degree but may be detected in amniotic fluid samples.
        • Mild cases show increased fetal red blood cell production sufficient to maintain the fetal circulation.
        • Extramedullary hematopoiesis is seen in the liver and spleen
        • The child is born pale and variably anemic.
        • Hepatosplenomegaly may be present. .(MCQ)
        • Severe cases present with severe anemia and hypoxia leading to fetal organ failure.
        • Fluid moves into the extravascular spaces, resulting in massive, generalized edema (hydrops fetalis). .(MCQ)
        • Unconjugated hyperbilirubinemia (jaundice) develops.
        • Bilirubin also deposits in the brain, primarily in the basal ganglia (ker- nicterus). .(MCQ)
        • Treatment includes exchange transfusion and phototherapy, which oxidizes bilirubin into nontoxic, water-soluble molecules.
        • RhoGAM
        • Rh-negative mothers carrying Rh-positive fetuses are treated prenatally at 28 weeks and shortly after delivery  in <72 hours with anti-D Rhesus immune globulin (RhoGAM). .(MCQ)
        • RhoGAM prevents sensitization by binding to fetal red cells in the maternal circulation, rendering them non-antigenic. .


      Blood Grouping Experiment – Amrita University
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