Final answer:
The highest priority action before beginning a transfusion of PRBCs is to check the identifying information on the unit of blood against the patient's ID bracelet to prevent transfusion reactions.
Step-by-step explanation:
Before beginning a transfusion of packed red blood cells (PRBCs), the action of highest priority to avoid an error during this procedure is A. Check the identifying information on the unit of blood against the patient's ID bracelet. This crucial step ensures patient safety by verifying that the blood type and Rh factor of the donor unit matches the patient's, preventing potentially fatal transfusion reactions.
It is essential to perform pretransfusion blood testing to match the donor's and recipient's ABO and Rh antigens correctly. Neglecting to verify the match before transfusion could lead to a hemolytic transfusion reaction (HTR), which can cause serious harm or even death to the patient.