A client is receiving a blood transfusion and develops chills, fever, and low back pain. What is the nurse's first action?

When a client develops chills, fever, and low back pain during a blood transfusion, these signs are classic indicators of an acute hemolytic transfusion reaction, which is a life-threatening emergency caused by ABO incompatibility. The priority action is to stop the transfusion immediately. Continuing to infuse incompatible blood — even at a slower rate — allows more antibody-antigen complexes to form, worsening hemolysis, which can progress to acute kidney injury, disseminated intravascular coagulation, and death. Stopping the transfusion immediately removes the source of harm. After stopping the transfusion, the nurse should maintain IV access with normal saline, notify the healthcare provider, and send the blood bag along with a blood sample from the client to the lab for analysis. Slowing the infusion rate is incorrect because it still exposes the client to incompatible blood. Notifying the healthcare provider is important but is a secondary action — safety must be established first. Administering acetaminophen might be appropriate for a febrile non-hemolytic transfusion reaction, but it must never be given before the transfusion is stopped, because the nurse cannot rule out the more dangerous hemolytic reaction at this point. The sequence of stopping the transfusion first is a foundational transfusion safety principle emphasized across all nursing curricula.