Donor: Healthy individual who spare his blood for a patient. Recipient: Sick individual who needs blood. Antigen: A macromolecule capable of inducing immune response in body e.g. proteins. Antibody: A kind of plasma protein that fight against specific antigen. Agglutination: is immunological reaction between antigen and antibody. Blood transfusion: Is process of transferring donor’s blood into recipient’s body.