2. What Is Latex Fixation Test?
• A latex fixation test, also called a latex agglutination test. • It is a antigen-antibody reaction
• Agglutination is a reaction of clumping together of antigen-bearing cells, microorganisms or
particles in the presence of specific antibodies (agglutinins) in a suspension.
• Reaction time for agglutination to occur is shorter compared to other antigen-antibody interactions.
• Latex agglutination makes use of latex particles which are built from different organic materials to a
desired diameter, and may be functionalized with chemical groups to facilitate attachment of molecules.
• soluble Ag/Ab are coated on inert particles-latex to develop sensitivity, specificity and easy to perform
this rapid test.
3. Principle
• In latex fixation/agglutination, antibodies are adsorbed to the latex particles (under
appropriate ionic and alkaline pH conditions) by binding to the Fc region of
antibodies leaving Fab region free to interact with antigen present in the applied
specimen. The use of smaller latex particle has improved the sensitivity and reagent
longevity of latex agglutination.
Latex coated with Ab
Ag
Visible Clumping ;Agglutination
4. Procedure
• Many latex agglutination tests are commercially available and are used to detect either
specific antigens or antibody against specific microbial and viral infections, autoimmune
diseases, hormones, drugs and serum proteins to diagnose various diseases.
• Clean Agglutination Cards • Disposable Mixing Sticks
• Negative Control
• Positive Control
• Latex particles sensitized with Ab/Ag
• Materials
• Prepared Patient Sample
5. Procedure
Re suspend the test latex by rapidly inverting the bottle several times. Dispence one drop of the Test latex into a
sepatate test circle for each specimen and control to be tested.
Allow all reagents to reach room temperature before use.
Dispense one drop of each well mixed control into a separate, test circle containing the test latex
Dispense one drop of each pretreated patient specimen (approximately 50 μl) into a test circle containing Test latex.
Thoroughly mix the specimen and Test latex, spreading over the entire area of the circle, with disposable Mixing
Sticks
Place the card on a clinical rotator set to rotate at 100 to 110 rpm for 5 minutes.
Immediately following the 5-minute rotation tilt the slide to obtain a flow pattern and carefully examine each circle
for any agglutination
7. Applications
Latex Fixation/Agglutination Test for Antibody Detection is used for detection of -
ASO (antistreptolysin O antibody). A diagnosis test for: • Acute rheumatic fever (2-3% Pharyngitis-Tonsilitis) ( Antigeng M) • Rheumatic heart
disease • Acute post streptococcal glomerulonephritis The antibodies level starts to rise in 1-3 weeks after streptococcal infection, peaks in 3-5 weeks, and then goes
back to insignificant level over 6-12 months, so a positive test can indicate current but more recent group A, C, and G streptococcal infection.>200IU =CLUMPING
most widely used method employed worldwide for detection of
C-reactive protein. (Detection limit of CRP by latex agglutination test is 0.6mg/dl.)
acute phase reactants (APRs)Whose plasma concentration changes in response to a variety of inflammation states including:Infection SurgeryTraumaSome cardiac
diseases Malignancy Tissue necrosis. rises rapidly (24-48 hours) after inflammation and its early return to normal levels after successful therapy make CRP the best
APR, suited for diagnostic purposes. infection with bacteria lead to higher CRP levels than viral diseases,
Latex agglutination tests are very popular in clinical laboratories. These tests are applied to the
detection of many infectious diseases.
• To detect microbial and viral infections, autoimmune diseases, hormones, drugs and serum proteins.
• To check for certain Ag/ Ab in a variety of bodily fluids including saliva, urine, cerebrospinal fluid, blood.
HCG Latex Agglutination Test
Latex agglutination test for pregnancy comprises the use of suspensions of polystyrene latex particles sensitized with anti-serum to human chorionic gonadotropin (hCG).
When mixed with urine or serum containing HCG, agglutination indicating a positive test for pregnancy. This glycoprotein hormone is released by placenta.
The HCG becomes detectable 6-12 days post conception. hCG is a dimer consisting of a 145 amino acid beta-subunit that is unique to hCG and a 92 amino acid alpha-subunit.
After synthesis, the alpha and beta-subunits are bonded with a noncovalent bond before being released into the circulation.
8. Advantages
•The size of the latex bead (0.8 μm or
larger) enhances the ease with which
the agglutination reaction is visualized.
•LAT is one of the most widely used tests
at present as it is very simple and rapid.
It is believed to have replaced many
other serological tests including
co-agglutination tests.
•They are inexpensive, relatively stable
and not subject to cross reactivity with
other antibodies.
•Levels of bacterial polysaccharides
detected by latex agglutination have
been shown to be as low as 0.1 ng/mL.
9. Limitations
•Because the pH, osmolarity, and ionic
concentration of the solution influence the
amount of binding that occurs, conditions under
which latex agglutination procedures are carried
out must be carefully standardized.
•Some constituents of body fluids, such as
rheumatoid factor, have been found to cause
false positive reactions in the latex agglutination
systems available.
•Some agglutination methods require specimens
to be pretreated by heating at 56°C or with
ethylenediaminetetraacetic acid (EDTA) before
testing making it a tedious process.
