What blood bank test is appropriate to perform to phenotype a patient's cells for the Fya antigen when anti-Fya (Anti-Fy^a) is present in their serum?

Indirect Antiglobulin Test (IAT) is the Appropriate Test for Phenotyping Fya Antigen

The indirect antiglobulin test (IAT) is the appropriate blood bank test to perform when phenotyping a patient's cells for the Fya antigen when anti-Fya is present in their serum. 1

Understanding Blood Group Antigen Phenotyping

When a patient has developed an antibody like anti-Fya, it's essential to determine whether their own red blood cells express the corresponding antigen. This process, called phenotyping, helps in:

1. Confirming the antibody's clinical significance
2. Guiding future transfusion strategies
3. Preventing hemolytic transfusion reactions

Why IAT is the Correct Choice

The IAT (option D) is the standard method for phenotyping red cell antigens because:

• It detects antibody binding to red cell antigens through the addition of anti-human globulin reagent
• It provides high sensitivity for detecting most clinically significant blood group antigens, including those in the Duffy blood group system 1
• It follows the American Society of Hematology guidelines which recommend extended red cell antigen profiling including Fya/Fyb typing 2

Why Other Options Are Not Appropriate

• Adsorption (option A): This technique is used to remove unwanted antibodies from serum, not to determine antigen presence on red cells. It's commonly used to remove autoantibodies to detect underlying alloantibodies 3, 4, but is not appropriate for phenotyping.

• Elution (option B): This procedure is used to recover antibodies bound to red cells, typically after a positive direct antiglobulin test (DAT). It's not used for initial phenotyping of antigens on red cells.

• DAT (option C): The direct antiglobulin test detects antibodies already bound to the patient's red cells in vivo. It doesn't determine the presence of specific antigens on red cells.

Practical Considerations for Fya Phenotyping

When performing Fya phenotyping using IAT:

1. Patient's red cells are washed to remove free antibodies
2. Commercial anti-Fya antisera is added to the patient's cells
3. After incubation and washing, anti-human globulin reagent is added
4. Agglutination indicates the presence of the Fya antigen (positive phenotype)
5. No agglutination indicates absence of the Fya antigen (negative phenotype)

Special Considerations

• If the patient has been recently transfused (within 3 months), serologic phenotyping may be inaccurate due to circulating donor cells 1
• In such cases, genotyping is preferred as it provides more accurate determination of the patient's true phenotype 1
• For patients with sickle cell disease who often develop anti-Fya, extended phenotyping or genotyping is particularly important 2

By correctly identifying the patient's Fya status through IAT, appropriate antigen-negative units can be selected for future transfusions, preventing hemolytic transfusion reactions and ensuring optimal patient care.