Role of Blood Groups in Transfusion

Immunogenicity and Antigen Prevalence must be considered to understand why certain antibodies (like anti-D, anti-K, anti-c) are common and clinically significant, why others (like anti-k, anti-U) are rare but problematic when they occur, and why still others (like anti-Wr^a) might be potent but easier to manage from a supply perspective. This combined understanding guides transfusion strategies, donor screening, and patient management to ensure the safest possible transfusions

• Immunogenicity: tells us the risk of antibody formation if exposed
• Antigen Prevalence: tells us the likelihood of exposure and the difficulty of finding compatible blood once an antibody exists

Immunogenicity: The Power to Provoke

• What it is: The inherent ability of a specific blood group antigen to stimulate an antibody response (alloimmunization) when introduced into someone lacking it
• Think: How “strong” or “noticeable” is this antigen to the recipient’s immune system?
• Key Players
  • Highly Immunogenic: D, K, c, E, C, e, Jk^a/Jk^b, Fy^a/Fy^b (Proteins are generally more immunogenic)
  • Less Immunogenic: Many other antigens provoke antibodies less frequently upon exposure
• Impact: Determines the likelihood that exposure to an incompatible antigen will actually lead to antibody formation. High immunogenicity = higher chance of making an antibody after exposure

Antigen Prevalence: How Common It Is

• What it is: The frequency (% of people) with which a specific blood group antigen is found in a given population
• Think: How likely is a random donor/recipient to have this antigen?
• Key Categories
  • High Prevalence (>99%): k, Kp^b, Lu^b, U, Vel, etc
  • Low Prevalence (<1-10%): K, Kp^a, Lu^a, Wr^a, etc
  • Intermediate/Variable Prevalence: ABO, Rh (D, C, c, E, e), Kidd, Duffy, MNS (M, N, S, s). Crucially, these vary significantly between different ethnic populations
• Impact
  • Determines the likelihood of exposure to an incompatible antigen during random transfusion
  • Determines the ease or difficulty of finding antigen-negative blood once an antibody has been formed

## The Interplay: Why Both Matter Together

Considering immunogenicity and prevalence together allows us to predict clinical challenges:

• High Immunogenicity + High Prevalence Antigen (e.g., k, U, Lu^b)
  • Immunogenicity: High (if exposed, likely to make Ab)
  • Prevalence: High (most people have it)
  • Result: Antibody formation is rare (because few people lack the antigen to be stimulated), BUT if an antibody is formed, finding compatible (antigen-negative) blood is extremely difficult. The prevalence dominates the compatibility challenge
• High Immunogenicity + Low Prevalence Antigen (e.g., K, Wr^a)
  • Immunogenicity: High (if exposed, likely to make Ab)
  • Prevalence: Low (few people have it)
  • Result: Antibody formation is relatively common among those exposed (due to high immunogenicity), BUT finding compatible (antigen-negative) blood is usually easy (because most donors lack the antigen). The immunogenicity drives the risk upon exposure
• High Immunogenicity + Intermediate Prevalence Antigen (e.g., D, c, E, Jk^a, Fy^a)
  • Immunogenicity: High/Moderate
  • Prevalence: Intermediate/Variable
  • Result: Antibodies are frequently encountered in transfusion services. Finding compatible blood ranges from easy to moderately difficult, depending on the specific antigen’s frequency in the relevant donor population. Both factors significantly impact clinical practice. This is why matching for D is standard, and matching for other Rh/K antigens is common for chronically transfused patients
• Low Immunogenicity Antigen (Regardless of Prevalence)
  • Immunogenicity: Low
  • Prevalence: Can be high, low, or intermediate
  • Result: Antibody formation is less common, even upon exposure. While compatibility testing is still required, these antigens cause fewer clinical problems overall compared to highly immunogenic ones