ABO system of blood groups and its basis, and erythroblastosis foetalis. (2024/10 Marks)

Introduction

The ABO system of blood groups is a classification system based on the presence or absence of specific antigens on the surface of red blood cells. This system was discovered by Karl Landsteiner in 1900 and is one of the most important blood group systems in humans. 

ABO Blood Group System

• Discovery and Basis
  
  • Identified by Austrian immunologist Karl Landsteiner in 1901. 
  • Determined by the presence or absence of antigens A and B on red blood cells.
• Blood Group Classifications
  
  • Type A: Presence of A antigens; anti-B antibodies in plasma.
  • Type B: Presence of B antigens; anti-A antibodies in plasma.
  • Type AB: Presence of both A and B antigens; no anti-A or anti-B antibodies in plasma.
  • Type O: Absence of A and B antigens; presence of both anti-A and anti-B antibodies in plasma.
• Inheritance Patterns
  
  • Controlled by a single gene with three alleles: I^A, I^B, and i.
  • I^A and I^B are dominant over i; I^A and I^B exhibit codominance.
  • Genotypes determine phenotypes:
    
    • I^A I^A or I^A i → Type A
    • I^B I^B or I^B i → Type B
    • I^A I^B → Type AB
    • ii → Type O
• Clinical Significance
  
  • Critical in blood transfusions to prevent hemolytic reactions.
  • Influences organ transplantation compatibility.
  • Impacts maternal-fetal compatibility during pregnancy.

Erythroblastosis Fetalis (Hemolytic Disease of the Newborn)

• A condition where maternal antibodies attack fetal red blood cells, leading to anemia and jaundice in the newborn. 
• Causes
  
  • Rh Incompatibility: Occurs when an Rh-negative mother carries an Rh-positive fetus.
    
    • Maternal immune system produces anti-Rh antibodies after exposure to fetal Rh-positive blood cells.
    • These antibodies cross the placenta in subsequent pregnancies, attacking fetal red blood cells.
  • ABO Incompatibility: Less common; typically occurs when a mother with blood type O carries a fetus with blood type A, B, or AB.
    
    • Maternal anti-A or anti-B antibodies can cross the placenta and attack fetal red blood cells. 
• Symptoms
  
  • Anemia in the newborn.
  • Jaundice (yellowing of the skin and eyes).
  • Enlarged liver and spleen.
  • In severe cases, hydrops fetalis (abnormal accumulation of fluid in fetal compartments).
• Diagnosis
  
  • Blood tests to detect maternal antibodies.
  • Ultrasound to assess fetal well-being.
  • Amniocentesis to measure bilirubin levels in amniotic fluid.
• Treatment
  
  • Intrauterine Blood Transfusion: Transfusion of Rh-negative blood into the fetus to manage anemia.
  • Early Delivery: Induced labor if the fetus is mature enough to survive outside the womb.
  • Postnatal Care: Phototherapy to reduce bilirubin levels and prevent jaundice.
  • Exchange Transfusion: Replacement of the newborn's blood to remove antibodies and excess bilirubin.
• Prevention: Administration of Rh immunoglobulin (RhoGAM) to Rh-negative mothers during and after pregnancy to prevent sensitization. 

Conclusion

The ABO system of blood groups is a crucial classification system that plays a significant role in blood transfusions and organ transplants. The basis of the ABO system and the potential complications like erythroblastosis foetalis is essential for healthcare professionals to provide safe and effective care for patients.