Latex Agglutination is a type of passive agglutination which employs latex particles as carrier of antigen or antibodies. In this test, many antibody or antigen molecules are bound to latex beads (particles), which increases the number of antigen-binding sites. If corresponding antigen or antibody is present in a test specimen, antigen antibody bind and form visible, cross-linked aggregates. Latex agglutination can also be performed with antigen conjugated to the beads for testing presence of antibodies in a serum specimen.
Latex agglutination is observed when a sample containing specific antigen (or antibody) is mixed with an antibody (or antigen) which is coated on the surface of latex particles. It is a clinical method to detect certain antigens or antibodies in a variety of body fluids such as blood, saliva, urine and cerebrospinal fluid etc.
Antibody molecules can be bound in random alignment to the surface of latex (polystyrene) beads. Antigen present in a specimen being tested binds to the combining sites of antibody exposed on the surfaces of latex beads, forming cross- linked aggregates of beads and antigen.
The size of beads (0.8µm or larger) enhances the ease with which agglutination reaction is recognized. Levels of bacterial polysaccharides detected by latex agglutination have been shown to be as low as 1.0 ng /ml because pH, osmolarity and ionic concentration of solution influence amount of binding that occurs. Conditions under which agglutination procedures are carried out must be carefully standardized.
Additionally, some constituents of body fluids such as rheumatoid factor, have been found to cause false- positive reactions in this test. To counteract this problem, all specimens are recommended to be treated by boiling or with Ethylene diamine tetra-acetic acid (EDTA) before testing.
Commercial test systems are usually performed on cardboard cards or glass slides and manufacturer’s recommendations should be followed precisely to ensure accurate results.
Latex tests are used in clinical laboratories to detect antigen to Cryptococcus neoformans in CSF or serum and to confirm the presence of beta- hemolytic Streptococcus form culture plates. Latex tests are also available to detect Streptococcus agalactiae, Clostridium difficile toxins A and B and rotavirus.
- Reactions are graded on a 1+ to 4+ scale, with 2+ usually the minimum amount of agglutination seen in a positive sample.
- Control latex (coated with antibody form same animal species from which specific antibody was made) is tested alongside test latex. If the patient specimen or the culture isolate reacts with both the test and control latex, the test is considered non-specific and therefore uninterpretable.
Latex agglutination inhibition test
The inhibition test relies on competition for antibody between a latex- drug conjugate and any drug that may be present in sample (mostly urine).
A common example of latex inhibition includes testing urine sample for presence of specific drug. Urine sample is placed in mixing well of a slide containing antibody reagent, buffer and latex reagent.
- If a drug is absent, latex- drug conjugate binds to antibody and forms large particles that agglutinate. Therefore agglutination is evidence for absence of drugs in urine specimen.
- If a drug is present in urine sample, it competes with latex conjugate for small amount of available antibody. A sufficient quantity of drug will prevent formation of clumping and a positive urine sample does not change appearance of test mixture.
Advantages of latex agglutination
- Low individual test cost.
- Ability to obtain semi quantitative results.
- Relatively short time to obtain results.
- Need to careful to interpret marginal results.
- Less specificity due to interfering substances in many assays.
Download Link: Latex agglutination Reaction.pdf