Latex Agglutination Tests
Latex agglutination tests are very popular in clinical laboratories. These tests have been applied to the detection of over 100 infectious diseases, and many other applications are currently available.
The first description of a test based in latex agglutination was the Rheumatoid Factor Test proposed by Singer and Plotz in 1956. Since then, tests to detect microbial and viral infections, autoimmune diseases, hormones, drugs and serum proteins have been developed and marketed by many companies worldwide. New latex applications and technologies are still being devised and applied to new analyses.
In latex agglutination procedures, an antibody (or antigen) coates the surface of latex particles (sensitized latex). When a sample containing the specific antigen (or antibody) is mixed with the milky-appearing sensitized latex, it causes visible agglutination.
The degree of agglutination plotted as a function of agglutinant concentration follows a bell-shape curve similar to the precipitin one. Latex particles are used to magnify the antigen - antibody complex.
Many of the latex agglutination tests developed are performed manually and the agglutination is detected by visual observation.
Although quite useful in the laboratory and cheap due to the absence of equipment needs, these manual assays suffer from lack of consistency in endpoint readouts. It has been established that about 100 clumps must be seen to determine agglutination, and that these clumps must be of about 50 pm in size to be seen by eye.