What is the most common symptom of an adverse reaction to a blood transfusion?

The most common symptom of an adverse reaction to a blood transfusion is fever and chills. This symptom often occurs due to the body's immune response to the donor blood, which may be recognized as foreign. The immune system reacts to antibodies present in the transfused blood, leading to the release of pyrogens—substances that induce fever. This reaction can sometimes accompany other symptoms, but fever and chills are the hallmark indicators that a transfusion reaction is occurring. Recognizing this symptom is vital for healthcare providers, as it prompts immediate assessment and intervention to ensure patient safety.