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Rh Factors

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  • The Rh Factors grouping system, also known as the Rhesus blood group system, is the second most significant blood group system after the ABO system.

  • It was first discovered in 1940 by Karl Landsteiner and Alexander Wiener during experiments with the blood of rhesus monkeys, which is how the system got its name.

  • The Rh system is particularly important in blood transfusion medicine, pregnancy, and certain medical conditions.

Pictorial representation of Rh Factors
Pictorial representation of Rh Factors

Components of the Rh System:

  • The Rh blood group system is based on the presence or absence of the Rh antigen, also known as the Rh factor, on the surface of red blood cells (RBCs).

  • The most significant Rh antigen is the D antigen.

Rh Antigens:

  • D Antigen: The most immunogenic and clinically important antigen in the Rh system.

  • Other Antigens: There are other Rh antigens, such as C, c, E, and e, but the D antigen is the primary focus due to its strong immunogenicity.

Rh Status:

1. Rh Positive (Rh⁺):

  • Presence of D Antigen: Individuals have the D antigen on the surface of their RBCs.

  • Frequency: Approximately 85% of the population is Rh positive.

2. Rh Negative (Rh⁻):

  • Absence of D Antigen: Individuals lack the D antigen on the surface of their RBCs.

  • Frequency: About 15% of the population is Rh negative.

Clinical Significance of the Rh Factors:

Blood Transfusions:

  • Compatibility: Rh status must be matched during blood transfusions to prevent hemolytic reactions. An Rh negative individual should not receive Rh positive blood, as their immune system may produce anti-D antibodies that can attack the transfused RBCs.

  • Universal Donor and Recipient:

    • Universal Donor for Rh System: Rh negative blood can be given to both Rh negative and Rh positive recipients.

    • Universal Recipient for Rh System: Rh positive individuals can receive Rh positive or Rh negative blood.

Pregnancy Considerations:

  • If an Rh-negative woman is pregnant with an Rh-positive baby, she may develop antibodies against the baby's blood (Rh sensitization).

  • This is particularly a concern in subsequent pregnancies with an Rh-positive baby, as the mother's antibodies can attack the fetal red blood cells.

  • To prevent this, Rh-negative pregnant women often receive Rh immunoglobulin (RhIg) injections.


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