Antiglobulin

Antiglobulin refers to antibodies directed against human globulins, particularly immunoglobulins or complement components, used in laboratory testing to detect immune-mediated processes. The antiglobulin test, commonly called the Coombs test, employs anti-human globulin (AHG) to reveal antibodies or complement attached to red blood cells or present in serum. There are two main forms: direct antiglobulin test (DAT) and indirect antiglobulin test (IAT).

The direct antiglobulin test detects in vivo sensitization of red blood cells. Patient red cells are incubated with AHG; if IgG antibodies or complement fragments (such as C3d) are bound to the cells, the AHG causes visible agglutination. DAT is used to diagnose autoimmune hemolytic anemia, to investigate hemolytic transfusion reactions, and to assess neonatal or hemolytic disease of the newborn.

The indirect antiglobulin test detects antibodies in patient serum. Serum is incubated with test red cells bearing known antigens; if alloantibodies are present, they bind the cells. After washing, AHG is added to reveal bound antibodies by agglutination. IAT is used for antibody screening before transfusion, antibody identification, and prenatal testing for antibodies that could affect fetal red cells.

Reagents come in monospecific forms (anti-IgG or anti-C3d) and polyspecific forms (anti-IgG plus anti-C3d). AHG reagents are integral to transfusion medicine and prenatal care, and the Coombs test remains a foundational tool for detecting immune-mediated red cell sensitization. Limitations include potential false positives or negatives and interference from certain clinical conditions or medications.