Serological test as widal for diagnosis of disease.pptx

Serological test as widal for diagnosis of disease.pptx

• 1.
  WIDAL TEST
• 2.
  HISTORY  It wasdeveloped by Farnand Widal in 1896.  Widal test is one of the oldest and most widley used serological test for diagnosis of enteric fever.  Salmonella antibodies start appearing in the serum at the end of first week of fever.  A rising titer of antibodies is indicative of enteric fever.
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  Principle  It isan agglutination test where H and O antibodies against S.typhi and S. Paratyphi A and B are detected.
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  ANTIGEN USED  Fourantigen are used. 1. O antigen of S.Typhi (TO) 2. H antigen of S.Typhi (TH) 3. H antigen of S. Paratyphi A (AH) 4. H antigen of S. Paratyphi B (BH)
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  METHODS OF WIDALTEST  Two types as follows:- 1. Slide widal test (Rapid, Screening & Qualitative) 2. Tube widal test (Quantitative)
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  Material OF WIDALTEST 1. Slide widal test 2. Tube widal test 3. Chemical reagent or antigens 4. Blood/serum 5. Normal saline 6. Mixer stickes 7. Timer
• 7.
  Slide widal test Mix one drop of patient serum & one drop of Ag (O,H,AH,BH) in respective circle on slide.  Mix properly & rotate for 1 min.  Examine for clump.  Put –ve & +ve control also.
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  Result  Positive:- Clumps Negative:- No clump.
• 9.
  Interpretation of slide widal SERUMVOLUME (In microlitres) APPROXIMATE TUBE TEXT TITRE 80µl 1:20 40µl 1:40 20µl 1:80 10µl 1:160 5µl 1:320
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  Tube widal test Following are 4 main steps:- i. Master dilution ii. Serial Dilution iii. Final dilution iv. Incubation
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  Master dilution  Takeone tube & prepare 1:10 dilution of serum called master dilution.  Add 1800 µl of normal saline + 200 µl of patient serum.
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  Serial Dilution  Take16 test tube & arrange in 4 rows.  Add 250 µl Normal saline in each test tube.  Add 250 µl master diluted serum in 1st vertical row only.  Do the serial dilution by transferring the 250 µl serum from 1st to 2nd vertical row 2nd to 3rd , 3rd to 4th & from 4th it will discard.  So, dilution in 1st, 2nd, 3rd, & 4th vertical row is 1:20, 1:40, 1:80, 1:160 respectively.
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  Final dilution  Add250 µl O, H, AH & BH Ag 1st, 2nd, 3rd, & 4th horizontal row respectively.  So, final dilution in 1st, 2nd, 3rd, & 4th vertical row is 1:40, 1:80, 1:160 and 1:320 respectively.  Put positive & negative control also.
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  incubation  Test tubeare incubated in water bath at 37ºC overnight. (16-18 Hr.)  Some authors recommend initial incubation at 50-55ºC for 2 Hr.
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  RESULT  O Agglutination:-Disc like clumps at bottom of tube.  H Agglutination:- spherical, granular, cotton woolly clumps at the bottom of test tube.  Positive;- Indicating enteric fever.  Negative:- No enteric fever.
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  Tube widal test
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  S.N O. Titre (O/H/AH/BH) INTERPRETATION 1 <40 Negative 2Any one 40 Kindly repeat the after one weak to see rise in titer 3 O-80 H/AH/BH-40<40 Could be Early Typhoid/Paratyphoid Fever Kindly repeat the after one weak to see rise in titer 4 O-40/<40 H/AH/BH-80 Could be past Typhoid/Paratyphoid Fever 5 O-80 Any one 160 Suggestive of Typhoid/Paratyphoid Fever 6 Any one 160 Suggestive of Typhoid/Paratyphoid Fever 7 O-160 Any one H-160 Significant for Typhoid/Paratyphoid Fever 8 Any one 320>320 Significant for Typhoid/Paratyphoid Fever 9 O-80/40/<40 Multiple H-80/160 Anamnestic Response with non Samonella organisms (Malara, Dengue, Influenza etc.)
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