Ring Precipitation Test
Definition
A technique in which antiserum is placed in a narrow capillary tube and antigen solution is layered carefully on top. A ring of white precipitate at the liquid interface indicates a positive reaction. Also called the Ascoli test or tube precipitin test.
- Also called
- Ascoli test, tube precipitin test
- Method
- Antigen layered over antiserum in a capillary tube
- Positive sign
- White precipitate ring at the interface
Common questions
Why has the ring precipitation test largely been superseded in modern labs?+
It requires careful layering technique to avoid mixing the two liquids prematurely, and it is less sensitive and slower to interpret than gel-diffusion methods like the Ouchterlony test, which is why many labs now prefer double-diffusion techniques.
What can cause a false negative in the ring precipitation test?+
Antigen or antibody concentrations outside the zone of equivalence, degraded reagents, or disturbance of the liquid interface during setup can all prevent a visible precipitate ring from forming even when a true reaction would otherwise occur.
Related terms
- Double Immunodiffusion (Ouchterlony)
- A gel diffusion method in which both antigen and antibody diffuse toward each other from separate wells in agar. Precipitin bands form...
- Equivalence Zone
- The range of antigen-to-antibody ratios at which binding sites on both molecules are maximally cross-linked, producing the largest lattice and the heaviest...
- Immunoelectrophoresis
- A two-step technique: proteins are first separated by electrophoresis in agar gel, then antiserum diffuses from a parallel trough and forms precipitin...
- Lattice Theory
- The structural explanation for precipitation proposed by Marrack in 1934. Multivalent antigens and bivalent antibodies can each bind more than one partner,...
- Precipitin
- An antibody that forms a visible precipitate when it reacts with its specific soluble antigen. The term is used interchangeably with precipitating...