18.6 Blood Typing - Anatomy and Physiology 2e

Learning Objectives

• Understand the physiological consequences of transfusion of incompatible blood.
• Compare and contrast ABO and Rh blood groups.
• Identify compatible blood groups for transfusion based on ABO types.
• Discuss the pathophysiology of hemolytic disease of the newborn.

Historical Context

• Blood transfusions were dangerous until the discovery of major human blood groups by Karl Landsteiner in 1900.
• Transfusion reactions occur when incompatible blood is transfused, leading to immune responses.

Antigens, Antibodies, and Transfusion Reactions

• Antigens: Substances that trigger immune responses if not recognized as "self."
  • RBC antigens are called isoantigens or agglutinogens.
• Antibodies: Proteins that attach to antigens, causing them to clump (agglutination).
  • Produced by B lymphocytes called plasma cells.
• Agglutination and Hemolysis:
  • Clumps of erythrocytes block blood vessels, leading to oxygen deprivation.
  • Hemolysis releases hemoglobin, which can overwhelm kidney capacity.
• Over 50 antigens identified in blood, but ABO and Rh are most significant.

The ABO Blood Group

• Determines presence/absence of A and B antigens (glycoproteins) on erythrocytes.
• Blood types: A, B, AB, O (genetically determined).
• Natural antibodies form against antigens:
  • Type A: anti-B antibodies.
  • Type B: anti-A antibodies.
  • Type AB: no antibodies.
  • Type O: anti-A and anti-B antibodies.

The Rh Blood Group

• Based on presence/absence of Rh antigen (specifically D antigen).
• Rh+: Presence of Rh D antigen.
• Rh-: Absence of Rh D antigen.
• Sensitization occurs after exposure to Rh antigen.
• Hemolytic disease of the newborn (HDN) from Rh incompatibility.

Hemolytic Disease of the Newborn (HDN)

• Occurs when Rh- individual is exposed to Rh+ antigens usually during childbirth.
• Subsequent Rh+ pregnancy can lead to agglutination and hemolysis of fetal RBCs.
• RhoGAM: Prevents development of Rh antibodies.
  • Administered during pregnancy and after birth to prevent HDN.

Determining ABO Blood Types

• Blood type determined using antibodies against A, B, and Rh antigens.
• Agglutination indicates presence of antigens.

Transfusion Protocols

• Best practice: Transfuse matching blood types.
• Universal Donor: Type O (lacks A and B antigens).
  • May still cause issues due to Rh and other antibodies.
• Universal Recipient: Type AB+ (no anti-A or anti-B antibodies).

Emergency Situations

• In emergencies, type O blood used to replace lost blood volume.
• Blood substitutes being developed to avoid compatibility issues.
• Saline solutions provide temporary volume replacement.

Key Notes

• Blood type compatibility is crucial to prevent adverse reactions.
• Proper cross matching and understanding of ABO and Rh systems essential.

Conclusion

Understanding blood typing and compatibility is critical for safe transfusions and preventing conditions like HDN. The discovery and application of blood group systems have revolutionized medical transfusion practices.