What D-positive (Rh D positive) red blood cell phenotype has the highest probability of being Fya (Duffy a antigen) negative?

D-Positive Red Blood Cell Phenotype with Highest Probability of Being Fya-Negative

The R2R2 (D+) phenotype has the highest probability of being Fya-negative, making it the correct answer (option D).

Understanding Blood Group Distributions and Duffy Antigens

The Duffy blood group system includes several antigens, with Fya and Fyb being the most clinically significant. When working with antibody screens showing possible anti-D and anti-Fya, understanding the relationship between Rh phenotypes and Duffy antigen distribution is crucial.

Duffy Antigen Distribution by Population

• The frequency of Duffy genes varies significantly across different populations 1:
  • Aboriginal populations have a high frequency of Fya
  • European Caucasians have a higher frequency of Fyb
  • Black populations have a high frequency of the Fy allele, which often results in the Fy(a-b-) phenotype

Rh Phenotypes and Correlation with Duffy Antigens

• R2R2 (D+C-E+c+e-) individuals are more likely to be Fya-negative because:
  • The R2 haplotype is more common in certain populations that also have a higher prevalence of Fya-negative phenotypes
  • There is genetic linkage between certain Rh haplotypes and Duffy expression patterns

Clinical Significance in Transfusion Medicine

Understanding this relationship is critical when working up complex antibody screens:

• Anti-Fya is approximately 20 times more common than anti-Fyb in transfusion reactions 1
• The American Society of Hematology recommends extended red cell antigen matching including Fya/Fyb for patients with sickle cell disease to prevent alloimmunization 2
• Having knowledge of which D-positive phenotypes are likely to be Fya-negative helps expedite compatibility workup for patients with multiple antibodies 3

Antibody Workup Strategy

When faced with a patient having both anti-D and anti-Fya antibodies:

1. First identify D-positive units that are likely to be Fya-negative (R2R2)
2. Confirm with specific antigen typing
3. This approach saves time compared to randomly testing units for both antigens

Common Pitfalls to Avoid

• Don't assume that all D-positive units will be problematic for a patient with anti-Fya
• Remember that the R2R2 phenotype, while more likely to be Fya-negative, still requires confirmation testing
• Extended phenotyping or genotyping is recommended for patients who may require multiple transfusions 3

This knowledge is particularly valuable when managing patients with multiple antibodies, as finding compatible units becomes increasingly challenging with each additional antibody specificity.