Recipient Serum That Reacted with One Out of Five Donor

Multiple Choice

Recipient serum that reacted with one out of five donor units in the AHG phase and where the antibody screen was negative is probably due to:

A) an alloantibody directed against a high-frequency antigen.
B) an alloantibody directed against a low-frequency antigen.
C) an alloantibody coating the recipient cells.
D) an ABO mismatch.