Name one severe adverse reaction that can occur during blood transfusion.

An acute hemolytic reaction is a severe adverse reaction that can occur during a blood transfusion, distinguished by the body's immune response attacking the transfused red blood cells. This reaction typically occurs when there is an ABO blood group incompatibility between the donor's blood and the recipient's blood, which can result in the destruction of the transfused red blood cells. Symptoms often manifest quickly, within minutes to a few hours after the transfusion begins, and may include fever, chills, back pain, dark urine, and in severe cases, renal failure or shock. Recognizing and managing acute hemolytic reactions promptly is critical to ensuring patient safety during blood transfusion procedures.