Antiglobulin (Coombs) test
Definition
A two-stage assay that detects IgG antibodies bound to red blood cells. The direct test detects in-vivo cell-bound IgG; the indirect test detects free IgG in serum by first incubating serum with red cells and then adding anti-human globulin to crosslink any IgG that has attached. Used when IgG antibodies are present but do not cause direct agglutination because of electrostatic repulsion.
Related terms
- Agglutination titre
- The reciprocal of the highest dilution of a serum or antigen solution at which visible agglutination still occurs. A titre of 1:64...
- Hemagglutination
- Agglutination specifically involving red blood cells as the antigen-bearing particles. Direct hemagglutination occurs when antibodies bind surface antigens naturally present on red...
- Low-ionic-strength saline (LISS)
- A reaction medium with reduced salt concentration used to enhance agglutination sensitivity, particularly for IgG antibodies. Lowering ionic strength reduces the electrostatic...
- Passive (indirect) agglutination
- An agglutination format in which a soluble antigen or antibody is adsorbed or covalently linked to a carrier particle (latex bead, tanned...
- Prozone (hook) effect
- A false-negative agglutination result caused by antibody excess. When antibody molecules outnumber antigen sites, each site is occupied by a single antibody...
Explained in
- Agglutination Reactions: Direct and Indirect MethodsA two-stage assay that detects IgG antibodies bound to red blood cells. The direct test detects in-vivo cell-bound IgG; the indirect test detects free IgG in s...