Particles.Tests based on agglutination of particles have been used as diagnostic tools for many years. Agglutination is defined as the clumping of particles to form insoluble aggregates. These tests employ latex particles, gelatin beads, colloidal particles, or preserved mammalian or avian blood cells to facilitate visualization of agglutination.
The components of an agglutination test consist of a test card or microscope slide and an agglutination solution with analyte-specific molecules that are attached to particles.

How it works
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To perform the classic version of the test, a specimen is placed on a microscope slide or in a microtest plate well, and then the carrier particles are added. The mixture is then stirred or agitated and incubated or allowed to settle for a few minutes. The results are determined by visually observing agglutination of the carrier particles as they bind to the specific analyte(s) in the sample. Depending on the test format, agglutination test results can be visualized with the naked eye or may require a microscope. (See "How it works" for more information on how these tests are performed and how they work.)

In strong reactions, the interpretation of results is simple, but in weak or marginal reactions, the interpretation can be difficult, and accurate results are possible only after much experience and practice. In the case of microwell plate assays, the pattern of particles that have settled needs to be interpreted to determine a result.

Advantages of agglutination methods include a low individual test cost, ability to obtain semiquantitative results, and a relatively short time to obtain results. Semiquantitative results can be obtained by performing 2- to 10-fold specimen dilutions.

Disadvantages include the need to carefully interpret marginal results and problems with specificity due to interfering substances in many assays.