Immunohematology

Immunohematology is a branch of hematology and immunology that studies antigen–antibody interactions in blood, focusing on red blood cells, platelets, plasma proteins, and related immune responses. Its primary aim is to ensure safe transfusion and to understand immune-mediated blood disorders. The field encompasses blood typing, antibody screening and identification, crossmatching, and the management of alloimmune and autoimmune phenomena affecting transfusion and pregnancy.

A central concept is the complexity of human blood group systems. The ABO and Rh (D) systems are the most clinically important, but many others—such as Kell, Duffy, Kidd, MNS, Lutheran, and Diego—also influence compatibility. Immunohematology addresses alloantibodies formed after exposure to foreign antigens (e.g., prior transfusion or pregnancy), autoantibodies, and conditions such as hemolytic disease of the newborn and various transfusion reactions. The discipline supports both transfusion medicine and aspects of transplantation and perinatal care.

Laboratory testing in immunohematology combines serologic and molecular approaches. Serologic methods include antibody screening, antibody identification, the direct antiglobulin test (DAT), indirect antiglobulin test (IAT), and crossmatching. Phenotyping and genotyping of blood group antigens inform extended matching, while adsorption, elution, and affinity techniques aid antibody characterization. Molecular typing complements serology for donor and recipient antigen profiles, particularly when serologic typing is inconclusive.

Clinical applications include selection and preparation of compatible blood components (red cells, platelets, plasma), leukoreduction and irradiation when indicated, and strategies to prevent alloimmunization. Immunohematology also plays a role in diagnosing and managing transfusion reactions, hemolytic disease of the newborn, and, in transplantation contexts, assessing HLA compatibility. Regulatory guidelines from bodies such as AABB and WHO help ensure safety and standardization.