Answered: Why is the Widal Test performed? What…

Biochemistry

9th Edition

ISBN:9781319114671

Author:Lubert Stryer, Jeremy M. Berg, John L. Tymoczko, Gregory J. Gatto Jr.

Publisher:Lubert Stryer, Jeremy M. Berg, John L. Tymoczko, Gregory J. Gatto Jr.

Chapter1: Biochemistry: An Evolving Science

Section: Chapter Questions

Problem 1P

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WIDAL TEST Principle: The test depends on the ability of antibody in the patient’s serum to agglutinate the stained bacterial antigens. When this occurs, the aggregates become clearly visible to the naked eye. Materials: Test tube 75 x 12 mm Physiological saline (0.9%) Incubator or water bath Slides Procedure: A. Rapid Slide Test Semi-Quantitative Method 1. Using a graduated pipette add the following amounts of serum to consecutive circles on a slide for each dilution under test. 0.08 ml, 0.04 ml, 0.02 ml, 0.01 ml and 0.005 ml 2. Thoroughly resuspend the antigen and add a drop to the appropriate circle on the slide. 3. Mix the drops and spread to cover the entire test circle. 4. Gently and evenly, rock and rotate the test slide for 1 minute then examine the slide for agglutination. 5. Results obtained correspond to tube agglutination titer of 1:20, 1:40, 1:80, 1:160, 1:320 respectively. 6. It is advisable to confirm a slide titration by the tube technique. B. Tube Agglutination Test 1. Prepare a rack of 10 tubes. Add 1.9 ml of saline to tube 1, and 1.0 ml of saline to each of the other tubes. 2. Add 0.1 ml of patient’s serum to tube 1. Mix well. 3. Withdraw 1.0 ml from tube 1 and transfer to tube 2. Continue serial doubling dilutions in this way until tube 9. Discard the 1.0 ml withdraw from tube 9. 4. Add 1 drop of thoroughly resuspended antigen suspensions to each tube in the rack. Do not dilute the suspensions for use. Tubes 1 – 9 now contain serum diluted from 1 / 20 to 1/ 5120. Tube 10 contains only saline and antigen and is the antigen control. 5. Mix well and incubate as follows and examine for agglutination. “O” titration 50 0C for 4 hours “H” titration 50 0C for 2 hour The antigen control should not show any agglutination Questions 1. Why is the Widal Test performed? What disease does it indicate? 2. Is the Widal test reliable? Enumerate the different bacteria that can cause false positive and false negative results.

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