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.
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 System:
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.