A blood bank has 10 units of Group O, Rh positive blood available. It should be easiest to find two units of compatible blood for which one of the following patients?

• A. anti-Le^a positive patient
• B. anti-E positive patient
• C. anti-K negative patient
• D. D positive patient

Answer: (A)

The key idea is transfusion compatibility: you must avoid any donor units that carry an antigen against which the patient has antibodies. For a patient with anti-Lea antibodies, the compatible units are Lea-negative red cells.

In a small stock of Group O, Rh positive units, Lea antigen expression varies among donors, and a meaningful number of these units do not express Lea on the red cells. That makes it relatively easy to pick two Lea-negative units from the ten available, without needing to exclude many units for other antigens.

If the patient had anti-E antibodies, you’d have to exclude E-positive units, and E is a fairly common antigen, so fewer units would be compatible. Similarly, anti-K antibodies would require K-negative units, and K antigen is present in a substantial portion of donors, limiting compatibility there. A patient who is simply D positive would be compatible with all the units in this stock, but the scenario emphasizes finding two Lea-negative units for someone with anti-Lea, which is typically feasible in a small O-positive pool.