Type II hypersensitivity reaction. Intravascular hemolysis (ABO blood group incompatibility) or extravascular hemolysis (host antibody reaction against foreign antigen on donor RBCs).

Presentation:- Fever- Hypotension- Tachypnea- Tachycardia- Flank pain- Hemoglobinuria (intravascular hemolysis)- Jaundice (extravascular hemolysis)

Timing: Within 1 hour