Pathophysiology
Clinical meaning
Febrile nonhemolytic transfusion reactions (FNHTRs) are the most common type of transfusion reaction, occurring in approximately 1-3% of RBC transfusions and up to 30% of platelet transfusions. Two primary mechanisms are involved: (1) Recipient antibodies against donor white blood cell antigens (HLA antibodies) - the recipient's immune system recognizes donor leukocytes as foreign and mounts a febrile response through cytokine release. This is most common in patients who have been previously transfused or who are multiparous. (2) Cytokine accumulation - during blood product storage, donor white blood cells release cytokines (IL-1, IL-6, TNF-alpha) into the product. When transfused, these preformed cytokines act on the hypothalamus to produce fever. The fever is defined as a temperature rise of 1 degree Celsius or greater above baseline, occurring during or within 4 hours after transfusion completion. While FNHTRs are not life-threatening, they are clinically significant because fever is also an early sign of the far more dangerous acute hemolytic transfusion reaction and bacterial contamination. Therefore, any fever during a transfusion must be treated as a potential emergency until a hemolytic reaction is ruled...