Adverse complications of transfusions can be classified into several categories:
- Immune-mediated transfusion reactions are those that trigger a response from the patient's immune system. Many transfusion reactions are mediated by the recipient's immune system. These reactions occur as a result of antigen-antibody interactions. Antibodies involved include those with specificity towards antigens on red cells, white cells, or platelets. In general, the immune responses occur in three stages:
- The immune system detects foreign material (antigen)
- The immune system processes the antigen
- The immune system mounts a response to remove the antigen from the body
- Non-immune mediated hemolytic transfusion reactions are caused by the physical or chemical destruction of transfused RBCs, bacterial contamination, circulatory overload, or citrate toxicity.
- Acute (immediate) reactions are those that occur during or within 24 hours after the transfusion. There is usually a rapid onset of symptoms and these reactions may be fatal.
- Delayed reactions occur weeks or months after the transfusion of blood or blood components.