Final answer:
During a blood transfusion, a nurse must immediately report a temperature of 101.3° F as it may indicate a possible transfusion reaction, potentially a serious and life-threatening condition. The correct option is 4.
Step-by-step explanation:
When administering a blood transfusion, a nurse should report a temperature of 101.3° F immediately. This could be indicative of a transfusion reaction, which is a potential emergency situation. Vital signs such as body temperature are critical in assessing a patient's condition.
A fever after a transfusion may suggest an incompatibility or allergic response to the transfused blood. This requires prompt intervention to prevent more serious complications, such as a hemolytic transfusion reaction that can be potentially lethal.