Final answer:
Febrile Non-Hemolytic Transfusion Reaction is caused by the immune response to donor white blood cell antigens, not by red blood cell destruction as seen in hemolytic reactions.
Step-by-step explanation:
The cause of Febrile Non-Hemolytic Transfusion Reaction (FNHTR) is an immune response to white blood cell antigens in the transfused blood. Unlike immediate hemolytic transfusion reactions (HTR), which are due to incompatibility between donor and recipient blood types and can result from ABO or Rh factor mismatches, FNHTRs are typically less severe and do not involve the destruction of red blood cells. FNHTRs are a reaction to the white cells, or leukocytes, from the donor blood, and the patient's immune system may react to these foreign white cells by releasing cytokines, which can cause fever and other symptoms.