A latex fixation test, also called a latex agglutination assay or test (LA assay or test), is an
assay
An assay is an investigative (analytic) procedure in laboratory medicine, mining, pharmacology, environmental biology and molecular biology for qualitatively assessing or quantitatively measuring the presence, amount, or functional activity of a ...
used clinically in the identification and
typing of many important
microorganisms. These tests use the patient's
antigen-
antibody immune response. This response occurs when the body detects a
pathogen and forms an antibody specific to an identified antigen (a protein configuration) present on the surface of the pathogen.
Agglutination tests, specific to a variety of pathogens, can be designed and manufactured for clinicians by coating
microbeads of
latex with pathogen-specific antigens or antibodies. In performing a test, laboratory clinicians will mix a patient's
cerebrospinal fluid,
serum
Serum may refer to:
*Serum (blood), plasma from which the clotting proteins have been removed
**Antiserum, blood serum with specific antibodies for passive immunity
* Serous fluid, any clear bodily fluid
* Truth serum, a drug that is likely to mak ...
or
urine with the coated latex particles in
serial dilutions with
normal saline (important to avoid the
prozone effect) and observe for
agglutination (clumping). Agglutination of the beads in any of the dilutions is considered a positive result, confirming either that the patient's body has produced the pathogen-specific antibody (if the test supplied the antigen) or that the specimen contains the pathogen's antigen (if the test supplied the antibody). Instances of
cross-reactivity (where the antibody sticks to another antigen besides the antigen of interest) can lead to confusing results.
Agglutination techniques are used to detect antibodies produced in response to a variety of
viruses and
bacteria, as well as
autoantibodies
An autoantibody is an antibody (a type of protein) produced by the immune system that is directed against one or more of the individual's own proteins. Many autoimmune diseases (notably lupus erythematosus) are associated with such antibodies.
Pr ...
, which are produced against the self in
autoimmune disease
An autoimmune disease is a condition arising from an abnormal immune response to a functioning body part. At least 80 types of autoimmune diseases have been identified, with some evidence suggesting that there may be more than 100 types. Nearly a ...
s. For example, assays exist for
rubella virus,
rotavirus, and
rheumatoid factor
Rheumatoid factor (RF) is the autoantibody that was first found in rheumatoid arthritis. It is defined as an antibody against the Fc portion of IgG and different RFs can recognize different parts of the IgG-Fc. RF and IgG join to form immune com ...
, and an excellent LA test is available for
cryptococcus.
[Howanitz and Howanitz, Laboratory Medicine. Published by Church Livingston; 1991: pp 825–828] Agglutination techniques are also used in definitive diagnosis of
group A streptococcal infection.
See also
*
References
External links
*
*
Description of the test
{{Immunologic techniques and tests
Blood tests
Immunologic tests
Medical tests