What is the most severe transfusion reaction attributed to?

The most severe transfusion reaction is attributed to ABO incompatibility. This type of reaction occurs when a patient receives blood from a donor with incompatible ABO blood type. When incompatible blood is transfused, the recipient's immune system recognizes the transfused red blood cells as foreign and mounts an immune response against them. This can lead to acute hemolytic transfusion reactions, which can cause symptoms such as fever, chills, back pain, and even more serious complications like acute kidney injury, shock, or death if not promptly addressed.

ABO incompatibility reactions are particularly severe because they involve the presence of pre-existing antibodies in the recipient's plasma that can quickly engage and destroy the transfused red blood cells, leading to rapid hemolysis. In contrast, other types of reactions, such as those caused by Rh incompatibility or febrile reactions, tend to be less severe in their immediate impact compared to the life-threatening potential of ABO mismatch. Non-ABO hemolytic reactions can occur but are generally not as acute or severe as those resulting from ABO incompatibility.