CONNON LATEX INVESTIGATIONS METHODS AND REPORTING

: principles of common Latex investigations methods and reporting

 Definitions of Terms 

·         latex agglutination-Visible clamping together of bacteria, cells or particles by an antigen combining with its specific antibodies.

·         precipitation –This is a test that involves reactions of soluble antigens. when it reacts with antibody it forms insoluble deposits(precipitate)

·         Immune-chromatographic test-

·         Flocculation- This is a test that involves reactions of soluble antigens. when it reacts with antibody it form loose clumps of  precipitate.(floccules)

·         Titre-The degree of antigen antibody reaction to show visible agglutination. This is the highest dilution of a serum which causes clumping  of microorganisms or particulate antigens.

ACTIVITY:

Define the following terms:

latex agglutination,precipitation,Flocculation,Immune chromatochraphic test

 Explain the principles of latex agglutination, flocculation tests and immune-chromatographic tests for antigen antibody reactions

LATEX AGGLUTINATION TESTS

PRINCIPLE

This test that involves specific antibody-antigen reaction.

 In this test polystyrene particles are coated with known antibodies or antigens.Eg.Antigen coated particles are used in  antistreptolysin O ttitration test.(ASOT).Antibody coated particles are used in detection of extracellular bacteria antigen in CSF.eg Cryptococcus neoformans.

Test that involves coated  particles are:

·         VDRL/RPR-The particles are coated with cardiolipin antigens.The particles are black in color hence carbon coated particles.

·         Widal test-The particles are coated with O and  H antigens that are coloured

·         Pregnancy test-The test involves polysterene particles coated with HCG hormone.

·         Rheumatoid factor test-The particles are coated with IgG antiglobulins(rheumatoid factors)

·         Hepatitis Test-The particles are coated with Hepatitis A,B C Antigens.

FLOCCULATION TESTS

PRINCIPLE

·         This test that involves antibody-antigen reaction. This is a test that involves reactions of soluble antigens. when it reacts with antibody it form loose clumps of  precipitate.(floccules)

IMMUNE-CHROMATOGRAPHIC TESTS

 Explain the following serological terms in relation to reporting of results: reactive, positive, non-reactive, negative,indeterminate

Reactive test -This is a test that shows presence of antibodies in a sample or specimen.

Non-reactive test- This is a test that shows absence of antibodies in a sample or specimen.

Positive and Negative -Final reporting/reading of a test after running the test with a positive and a negative  control and reads as the same as  controls.

Indeterminate-A test that is at border line. This means that the test is neither positive nor negative.

Invalid-A test that does not show any reading/reaction  with the control.(a plain strip)

 Key Points 

·         latex agglutination-Visible clamping together of bacteria, cells or particles by an antigen combining with its specific antibodies.

·         precipitation –This is a test that involves reactions of soluble antigens. when it reacts with antibody it forms insoluble deposits(precipitate)

·         Immune-chromatographic test-

·         Flocculation- This is a test that involves reactions of soluble antigens. when it reacts with antibody it form loose clumps of  precipitate.(floccules)

·         Titre-The degree of antigen antibody reaction to show visible agglutination. This is the highest dilution of a serum which causes clumping  of microorganisms or particulate antigens.

 List common specific immunology/serology investigation

·         VDRL/RPR,

·         HBs Ag,

·         Cryptococcus serum test,

·         Widal test,

·         pregnancy test,

·         rheumatoid factor test,

·         ICT

·         ASOT

 Explain the principle and reporting of each common  immunology/serology investigations according to SOP(2 HOURS)

SIGNIFICANCE OF INVESTIGATING TYPHOID FEVER

·         To confirm diagnosis of typhoid fever

·         To determine the carrier status who has recovered from typhoid fever.

·         Pyrexia of unknown cause(persistent high temperature)

WIDAL TEST  BY TILE METHOD,

Reagents

·         O-Antigens

·         H-Antigens

·         Controls – positive and negative

 Demonstration of the widal test  by tile method according to the SOP

·         Demonstrate of the pregnancy test according to the SOP.

 Performance of the widal test by tile method(Qualitative analysis) 

• Principle

Killed salmonella suspensions with O and H Ag reacts with corresponding Ab in the serum of the patient with infection and shows agglutation.

·         Procedure

o   Bring the test kit reagents to room temperature.

o   Mix the reagents before use

o   Pippette one  drop of O-Ag and H-Ag on  the circles on the tile or test cards.

o   Using a rubber teat and dropper pipette, dispense 1 drop (0.05ml) of sample on one of the test card circles labeled O and H.

o   Mix using the applicator stick

o   Dispense the positive and negative control sera in the same way and mix.

o   use your hands to rotate the test card for 1 minute..

o   Read the results macroscopically in a good light and check for agglutination.

o   Place all the materials in the bucket marked “INCINERATION”. 

NB: Each laboratory must determine the time necessary to perform the procedure (turnaround time).

·         Reporting results

o   Visible Agglutination indicates presence of salmonella Antibodies. Proceed to quantitative test( tube titration method)

o   No visible agglutination indicates absence of salmonella antibodies. Report as negative or non-reactive.

·         Limitations:

o   The test reagent must be stored at 2 – 8^oC and when in use place at room temperature before use.

o   Check carefully the expiry dates on the test kits.

·         Quality control

o   Always run positive and negative controls when performing the test, and make sure the control samples are reading correctly.