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Diagnosis ( Widal test et Rose Bengal plate test)
médecine (med1)
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2
nd
class
3
rd
lab.
Application of immunity in lab.
diagnosis
(WIDAL test & Rose Bengal plate test) "A test involving agglutination of typhoid bacilli when they are mixed with serum containing typhoid antibodies from an individual having typhoid fever; used to detect the presence of Salmonella typhi and S. paratyphi.“ Salmonella antigens include:- O= somatic antigen H= flagellar antigen Vi= capsular antigen
Slide Widal test:
Slide Widal test is more popular as it gives rapid results. SemiQualitative test: 1 drop of undiluted patient’s serum sample for the 2 antigens (O , H) is placed on the circled card. 1 drop of each of 2 salmonella antigens are added separately rotated gently for 1 min. Appearance of agglutination gives qualitative results. (semi quantitative test is repeated with dilutions of serum)
####### Tube agglutination test.
####### Detects anti O and H antibodies in serum
####### Diagnosis of Typhoid and Paratyphoid cases
####### Carriers of typhoid bacilli possess antibody against
####### the Vi antigen of S. typhi. (Vi titres seem to correlate
####### better with the carrier state than do O or H titres). For
####### this reason, the use of Vi agglutination for detection
####### of carriers was suggested.
4
WIDAL Test
Materials
• Antigens:
– Suspension of S. typhi "O" antigen, O
– Suspension of S. typhi "H" antigen, H
– Suspension of S. paratyphi A "H" antigen, PA
– Suspension of S. schottmuelleri "H" antigen, PB
• Antibody: serum of suspected patient
• Normal saline
• Test tubes and pipettes
1 2 3 4 5 6 7
O
H
PA
PB
PROCEDURE
PROCEDURE
- Make the mark of tubes
- Dilute patient’s serum 1:10 (0 ml serum + 0 ml saline).
- Add reagents as the following: Reagent (ml) 1 2 3 4 5 6 7 Saline 0 0 0 0 0 0 0. 1:10 Patient serum 0 0 0 0 0 0 discard Serum dilution 1:20 1:40 1:80 1:160 1:320 1:640 - Bacterial suspension 0 0 0 0 0 0 0. Final serum dil. 1:40 1:80 1:160 1:320 1:640 1:1280 -ve Bacteria suspension: O H PA PB Shake several times, put it in 37 0 C water bath for 16-18 hours.
####### Then let it stand at room temperature over night.
Agglutination how it appears after
reactivity
####### Observed for agglutination:
####### H : Loose , cotton woolly clumps;
####### O : Compact Fine granular agglutination;
####### Supernatant should be clear;
How do you read Widal test results for
typhoid fever?
- The highest dilution of the patients serum in
which agglutinations occurs is noted.
- Agglutination in dilution up to <1:60 is seen
in normal individuals.
- Agglutination in dilution 1:160 is suggestive of
Salmonella infection.
- Agglutination in dilution of >1:320 is
confirmatory of Enteric fever.
####### The Rose Bengal test (RBT) is a simple, rapid slide-type
####### agglutination assay performed with a stained Brucella
####### abortussuspension at pH3–3 and plain serum.
####### Although the overall sensitivity reported for RBT varies
####### widely, with the use of good quality antigens made by
####### experienced or reference laboratories, the sensitivity of RBT
####### can increased
It is often used as a screening test in human brucellosis and would be optimal for small laboratories with limited means. False-negative reactions occur especially in the early stages of acute infection. Procedure of Rose Bengal Plate Test: Test Serum (0 ml) is mixed with an equal volume of antigen on a white tile or enamel plate to produce a zone approximately 2 cm in diameter. The mixture is agitated gently for four minutes at ambient temperature, and then observed for agglutination. Any visible reaction is considered to be positive.
Diagnosis ( Widal test et Rose Bengal plate test)
Course: médecine (med1)
University: Université Sidi Mohamed Ben Abdellah de Fès
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