Which of the following is required for packed red blood cell (RBC) transfusions but not for platelets?

Packed red blood cell (RBC) transfusions require matching of the Rh factor to prevent hemolytic reactions, which can occur if an Rh-negative patient receives Rh-positive blood. This is crucial because the presence of Rh antigens on the RBCs of transfused blood can trigger an immune response in the patient if they are Rh-negative.

While ABO matching is also necessary for packed RBC transfusions to ensure compatibility, it’s not the only factor at play, as Rh factor matching is specifically emphasized in the question.

In contrast, platelet transfusions typically do not require Rh factor matching unless it's for a female of childbearing age, where there may be concerns regarding sensitization. Platelet transfusions focus more on ABO matching rather than Rh typing.

Thus, the need for Rh factor matching specifically for packed RBC transfusions highlights why it's considered a unique requirement compared to the protocols surrounding platelet transfusions.