Final answer:
The nurse should stop the blood transfusion immediately upon a patient reporting itching and hives, which are signs of an allergic reaction, potentially indicating the onset of a more severe reaction.
Step-by-step explanation:
If a patient reports itching and has hives after beginning a transfusion of packed red blood cells, the nurse should stop the blood transfusion immediately as the first action. This is indicative of an allergic reaction, which may be the onset of a more severe transfusion reaction, such as a hemolytic transfusion reaction (HTR). Once the transfusion has been stopped, the nurse should follow proper protocols, which often include monitoring the patient's vital signs, informing the physician, administering medications such as antihistamines if ordered, and preparing to take additional emergency measures if necessary. It's important to document the findings, but patient safety is the priority, and thus, stopping the transfusion should precede documentation. Administering an antihistamine or slowing the transfusion rate may be subsequent actions after stopping the transfusion and evaluating the patient's response.