#widal_test #widal_test_in_hindi
What is widal test
Widal test practical
Widal test in hindi
Qualitative widal test
Widal test by slide method
Slide Agglutination test
Quantitative Widal test
Tube method of widla test
Widal Test- Introduction, Principle, Procedure,
COMMON SEROLOGICAL TEST
Some of the standard serological tests are discussed.
Widal test
Principle: This test is advised for antibodies in patients’ serum against Enteric bacilli to diagnose enteric or typhoid fever.
Sample
The serum of patients is needed.
Procedure:
Qualitative
Quantitative
This can be done by
Slide method
Tube method
Antigens
Salmonella groups A, B, C, D, and E and Paratyphi A, B, C.
Salmonella Typhi antigens are:
O-Antigen (Somatic Antigen):- These are 0-17 groups. 95% fall in group A, B, C, D, and E.
O-Ag rises in 50% of the cases by the first week. It disappears in 6-12 months. This is diagnostic for acute infection.
H-Antigen (Flagellar Ag).
H-Ag rises slowly and disappears after many years.
V1-Virulence antigen. This is also a surface antigen. this is used to find the carrier state.
Precautions
No value if done before 7 days of the onset of fever. Two or preferably more tests are done every 3-5 days to see a rising titer.
Many people without the disease have agglutinin in low titer.
The immunized person will also show agglutinin (antibodies).
There will be a significant rise after 7-10 days.
The anamnestic reaction will show negative results in low dilution and will be positive in high dilution.
The test has to be done with a battery of antigens.
The slide test is suitable for screening, but confirmation should be done by tube method.
Interpretation
The history of patients and discussions with physicians will be helpful.
A single test is not diagnostic.
In a vaccinated case, antibodies may be present. So a significant level is a four-fold rise in O-Ag or at least O Ag is 1:80.
Antibiotic use prevents the rise in antibody levels.
Negative Result
When there is no agglutination
Blood was drawn early before 7 days.
A negative test does not rule out an enteric fever.
Positive Result
Indicate infection.
In-person with a history of vaccination.
A high titer of H-Ag indicates recent/past disease or vaccine.
Introduction of Widal Test
Widal Test is an agglutination test which detects the presence of serum agglutinins (H and O) in patients serum with typhoid and paratyphoid fever.
When facilities for culturing are not available, the Widal test is the reliable and can be of value in the diagnosis of typhoid fevers in endemic areas.
It was developed by Georges Ferdinand Widal in 1896.
The patient’s serum is tested for O and H antibodies (agglutinins) against the following antigen suspensions (usually stained suspensions):
S. Typhi 0 antigen suspension, 9, 12
S. Typhi H antigen suspension, d
S. Paratyphi A 0 antigen suspension, 1, 2, 12
S. Paratyphi A H antigen suspension, a
S. Paratyphi B 0 antigen suspension, 1, 4, 5, 12
S. Paratyphi B H antigen suspension, b, phase 1
S. Paratyphi C 0 antigen suspension, 6, 7
S. Paratyphi C H antigen suspension, c, phase 1
Salmonella antibody starts appearing in serum at the end of first week and rise sharply during the 3rd week of endemic fever. In acute typhoid fever, O agglutinins can usually be detected 6-8 days after the onset of fever and H agglutinins after 10-12 days.
It is preferable to test two specimens of sera at an interval of 7 to 10 days to demonstrate a rising antibody titre.
Salmonella antigen suspensions can be used as slide and tube techniques.
Principle of Widal Test
Bacterial suspension which carry antigen will agglutinate on exposure to antibodies to Salmonella organisms. Patients’ suffering from enteric fever would possess antibodies in their sera which can react and agglutinate serial doubling dilutions of killed, coloured Salmonella antigens in a agglutination test.
Preparation of Widal Antigens
H suspension of bacteria is prepared by adding 0.1 per cent formalin to a 24 hours broth culture or saline suspension of an agar culture.
For preparation of O suspensions of bacteria, the organisms is cultured on phenol agar (1:800) to inhibit flagella.
Standard smooth strains of the organism are used; S Typhi 901, O and H strains are employed for this purpose.
The growth is then emulsified in small volume of saline, mixed with 20 times its volume of alcohol, heated at 40° C to 50° C for 30 minutes and centrifuged.
The antigens are treated with chloroform (preservative) and appropriate dyes are added for easy identification of antigens
Procedure of Widal Test
SLIDE TEST
Place one drop of positive control on one reaction circles of the slide.
Pipette one drop of Isotonic saline on the next reaction cirlcle. (-ve Control).
Pipette one drop of the patient serum tobe tested onto the remaining four reaction circles.
Add one drop of Widal TEST antigen suspension ‘H’ to the first two reaction circles. (PC & NC).
Add one drop e place 5, 10, 20.
21 июн 2022
