Agglutination Titre
Definition
The reciprocal of the highest dilution of a serum or antigen solution at which visible agglutination still occurs. A titre of 1:64 means the endpoint is at a 64-fold dilution. Higher titres indicate higher concentrations of the reactive antibody or antigen. Serial two-fold dilutions (1:2, 1:4, 1:8, ...) are the standard method for determining titre.
- Definition
- Reciprocal of highest dilution still showing visible agglutination
- Example
- Titre of 1:64 means endpoint at 64-fold dilution
- Meaning of higher titre
- Higher concentration of reactive antibody or antigen
- Standard method
- Serial two-fold dilutions (1:2, 1:4, 1:8...)
Common questions
Why use two-fold dilution steps rather than, say, ten-fold?+
Two-fold steps give finer resolution around the true endpoint, since a ten-fold jump could skip over the dilution where agglutination just stops, whereas the smaller two-fold interval pins the endpoint down more precisely for a given number of tubes.
What can cause a falsely low titre reading in practice?+
Prozone effect, where antibody excess at low dilutions actually inhibits visible lattice formation, can make a strongly reactive sample appear to agglutinate weakly until it is diluted further, so titration series should extend past the expected endpoint.
Related terms
- Antiglobulin (Coombs) Test
- 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...
- 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...