8fb70e90_Transfusion_Reaction__Pathophysiology
[Reaction] Delayed haemolytic reaction [Symptom Description] Varying from sub-clinical reaction, to severe life-threatening reaction. Features include fever, lower than expected blood haemoglobin concentration with associated jaundice and urobilinogenuria. [Pathophysiology] 
Patients may develop antibodies to red cell antigens. Antibodies can occur naturally, or may arise as a consequence of previous transfusion or pregnancy. A delayed haemolytic reaction occurs when a patient develops an antibody directed against an antigen on transfused red cells. The antibody may cause shortened red cell survival, with clinical features of fever, jaundice and lower than expected haemoglobin following transfusion. Most delayed haemolytic reactions produce few symptoms and may go unrecognised; however there are reports of serious consequences in critically ill patients.
Transfusion Reaction
Pathophysiology