Granulocytes for transfusion should be:

Transfusing granulocytes requires consideration of several factors, and ABO compatibility with the recipient's serum is one of the most critical. Granulocyte transfusions are often used in patients with neutropenia or those who require increased white blood cell counts to fight infection. Incompatibility between the donor's and recipient's ABO blood groups can lead to transfusion reactions, which can manifest as hemolytic reactions if the recipient's immune system recognizes the donor blood cells as foreign. Therefore, ensuring ABO compatibility helps minimize the risk of adverse reactions following transfusion.

While the other factors, such as the administration through filters or the timing of the infusion, are also important, they do not directly address the immediate immunological compatibility that can affect patient safety and the success of the transfusion. Thus, ensuring that granulocytes are ABO compatible with the recipient's serum is essential for effective and safe transfusion therapy.