Biotechnology and Bioinformatics (1+1)

4.2.12.4.Latex agglutination test

Microsphere or latex agglutination tests (LATs) have been used since 1956, when Jacques Singer of Montefiore Hospital (Bronx, New York) developed a test for detection of reheumatoid factor.

Latex refers to the microscopic polymeric particles, which act as the base for various immunoassays and tests. They are made of polystyrene by the same emulsion polymerization process used for making synthetic rubber or latex. The particles are tiny, referred to as microspheres (diameter 0.015-40 mm), uniform (coefficient of variation 1-3 per cent), solid, and perfect, usually hydrophobic spheres.

Microsphere-based diagnostic tests (qualitative, yes/no results) and assays (quantitative results) are usually based upon the specific interaction of antigen (Ag) and antibody (Ab).

Sub-micron sized polystyrene (PS) microspheres, are used for solid support; Ab or Ag can be adsorbed to them.

These ‘sensitized’ microspheres then act to magnify or amplify the reaction, which takes place when they are mixed with a sample containing opposite reactant.

In simple particle agglutination, a positive test results when a drop of uniformly-dispersed milky-appearing Ab coated beads on a glass slide reacts with Ag in a drop of sample (whole blood, serum, antigen) to cause particle agglutination, i.e. clumping of microspheres, to look like curdled milk.

Alternatively, Ag-coated particles are agglutinated by a positive sample of Ab. Latex reagents are portable, useful every-where, rapid and efficient. Ideal for point-of-care use (field, on-site and ambulance), they can be run quickly and simply (2-3 min from the sample preparation), and diagnosis and treatment can commence promptly, before the advent of severe damage.

Since they can be run quickly and easily without instrumentation, they can replace other immunoassays like Radio-immunoassay (RIA) and Enzyme Linked Immunosorbent Assay (ELISA).

Ascencio (1990) developed a rapid particle agglutination assay using latex beads coated with connective tissue and serum protein s. This was evaluated for its ability to identify fibronectin, collagen cell surface receptors on Vibrio and Aeromonas strain s isolated from diseased fish, human infection and environment.