OVERVIEW:
What is the Widal test?
Widal test is a serological test for the diagnosis of typhoid fever. Widal test is based on the presence of IgG and IgM antibodies to a specific outer membrane protein of Salmonella Typhi.
Why is the Widal test done?
Widal test is done to detect, identify, and monitor the fever and other infections caused by Salmonella Typhi.
What does the Widal test measure?
Widal test detects the presence as well as antibody titres of IgG and IgM. Raised IgM level indicates recent infection whereas raised IgG level indicates remote infection.
What is Widal test used for?
Widal test is performed to make a presumptive diagnosis of Typhoid fever also known as Enteric fever.
What is the normal range for Widal test?
A single anti-TH titer > 1:160 and anti-TO titer > 1:80 indicates typhoid fever.
What is O and H in Widal test?
H is the flagellar and O is the somatic antigens of Salmonella Typhi.
How is Typhoid confirmed?
Typhoid fever is confirmed by testing blood, stool, or urine sample of the patient.
Is Widal test done on an empty stomach?
No fasting or any other special preparations are required for Widal test.
INTERPRETATIONS
If the antibody against Salmonella is present in the patient’s serum, it will react with the respective antigen in the reagent and give visible agglutination (clumping) on the test slide.
The highest dilution of the patient’s serum sample that gives a visible agglutination with the Widal test antigen suspensions is the antibody titer.
The serum sample which shows the titer of 1:80 or more for O agglutination and 1:160 or more for H agglutination indicates active infection. A rise in titers (4-fold or more) in the two blood samples taken 10 days apart confirms the diagnosis. Please note that different labs may have different reference values for the interpretation of the Widal test.
The interpretation of a Widal test is greatly influenced by the nature and extent of the patient’s previous contact with typhoid antigens. It can be either due to clinical or subclinical infection with typhoid or related organisms or from typhoid vaccination. The lesser extent of the previous contact, the greater the usefulness of the Widal test.
Widal test is performed to diagnose fever or other infections caused by Salmonella typhi.
