serum samples 4–6 days apart is more meaningful than single test

2. Patients on antibiotic therapy during the testing phase Check the history of the patient for administration of antibiotics

3. Insufficient serum dispensed leading to postzone effect Pipette exactly one drop of patient serum on each of the four reaction

circles, in case of slide test

In case of tube test carry out the dilutions carefully and correctly as

per the instructions given in the package insert

4. Hemolyzed, turbid or contaminated samples may have been used Avoid using hemolyzed, turbid or contaminated samples for testing

5. Serum stored for a long time is used for testing Fresh serum should be used for testing. However, in case of delay in

testing, the sample can be stored up to a maximum of 72 hours

6. Rotation of the slide too fast may break up agglutinating clumps,

which can lead to false negative in borderline cases

Rock the slide gently back and forth and observe for agglutination

macroscopically within one minute

7. Reagents not brought to room temperature. Cold reagents could

give false negative results

Bring all reagents and samples to room temperature before commencing the testing procedure

8. Insufficient reagent present in the vial Ensure that sufficient reagent is present in the vial before retrieving

the amount required for testing

9. Expired reagents are used for testing The performance of the reagents should be validated occasionally using the positive control provided. Good physiological saline may be

used as a negative control

630 Concise Book of Medical Laboratory Technology: Methods and Interpretations REDUCED WIDAL ANTIGEN SET: O AND H FOR

TUBE TESTS (VITAL WIDAL)

(Courtesy: Tulip Group of Companies)

Reagent

Vital Widal contains ready-to-use colored, smooth antigen

suspensions of the bacilli; S. typhi O and S. typhi H along

with a polyspecific positive control reactive with these

antigens. Vital Widal reagents are versatile and standardized for use in a modified tube test procedure for the

detection of S. typhi antibodies in the patient’s serum.

Each batch of regents undergoes rigorous quality

control at various stages of manufacture for its specificity

and performance.

Reagent Storage and Stability

1. Store the reagent at 2 to 8°C. Do not freeze.

2. The shelf-life of the reagent is as per the expiry date

mentioned on the reagent bottle labels.

Principle

When the colored, smooth suspension of attenuated Vital

Widal antigen suspensions are incubated with the patient’s

serum, anti-Salmonella antibodies if present in the patient’s

serum react with the antigen suspension to produce

an agglutination. Agglutination is a positive test result,

indicating presence of Salmonella antibodies in the patient’s

sample. No agglutination is a negative test result indicating

absence of Salmonella antibodies in the patient’s sample.

Note

In vitro diagnostic reagent for laboratory and professional

use only. Not for medicinal use.

The reagent contains 0.5% Phenol/0.3% Formaldehyde

as preservative. Avoid contact with skin and mucosa. On

disposal, flush with large quantities of water.

Sample Collection and Storage

1. No special preparation of the patient is required prior

to sample collection by approved techniques. Do not

use hemolyzed samples.

2. Clean and dry glassware free from detergents must be

used for sample collection.

3. Do not heat/inactivate the serum.

4. Though freshly collected serum is preferable, store

samples at 2 to 8°C in case of delay in testing.

Material Provided with the Kit

¾ Antigen suspension, S. typhi ‘O’

¾ Antigen suspension, S. typhi ‘H’

¾ Polyspecific positive control (goat)

¾ Color coded vial top squeeze droppers.

Additional Material Required

1. Test tubes/Kahn tubes (preferably)

2. Pipettes 0.1 mL, 1.0 mL

3. lncubator (37°C)

4. Pasteur pipettes

5. Isotonic saline.

Procedure

a. Tear off aluminium seals from the antigen vials. Fit on

to each antigen vial, vial top squeeze dropper.

b. Bring all reagents to room temperature before testing.

c. Shake antigens well before dispensing.

d. Carefully label test tubes for sample and reagent

identity.

e. Ensure squeeze dropper tips are wiped dry with clean

tissues, before recapping.

Tube Test Method

1. Take two sets of 8 Kahn tubes and test tubes and

label them as 1 to 8 for O and H antibody detection.

2. Pipette into tube No. 1 of all sets 1.9 mL of isotonic

saline.

3. To each of the remaining tubes (2 to 8 each set), add

1.0 mL of isotonic saline.