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What is a Widal Test?
The Widal test is a rapid diagnostic test used to identify the presence of infection with “Salmonella typhi” or “Salmonella paratyphi” bacteria. The test is based on the observation that typhoid patients have antibodies against Salmonella typhi in their blood, and therefore the bacteria will agglutinate when mixed with red blood cells from a healthy person. The presence of antibodies in the patient’s blood indicates that they are infected with Salmonella typhi and are likely to have typhoid fever. This test has no significant side effects and provides accurate test results most of the time at an affordable price.
What is the Widal test used for?
The Widal test is a blood test used to detect antibodies that are produced in response to a Salmonella typhi infection, which is the cause of typhoid fever. It is used to help diagnose a current or recent infection or to determine if an individual has had a previous typhoid infection.
How to read Widal test results and What is the Normal range in It?
The Widal test results are given as titre, which is a measure of the dilution at which the agglutination response occurs. The higher the titre, the more antibodies are present in the blood. The titres are given as a ratio, such as 1:20 or 1:80, which reflects the dilution at which the reaction happened.Â
The Widal test normal range is a titre that is less than 1:20 for both the O and H antigens of S. Typhi and S. paratyphi. A titre of 1:20 or above indicates the presence of antibodies and may suggest an ongoing or prior infection with the bacterium.
Frequently Asked Questions:
1. Why do I need the Widal test?
One of the reasons you might need to take this test is if you have been exposed to someone with typhoid fever and are unsure about your immunity status. Another reason might be if you have travelled outside your country and think that you might be at risk for developing typhoid fever.
2. What happens during the Widal test?
The Widal blood test is used to diagnose typhoid fever. It is a blood test that measures the presence and level of antibodies against two strains of Salmonella typhi, the bacteria that cause typhoid fever. During the test, whole blood from a patient is mixed with an antiserum containing antibodies against Salmonella typhi. If there are antibodies present in the blood sample from the patient, they will react with the antiserum and cause clumping or agglutination of red blood cells. This indicates that the person has typhoid fever.
3. How do I know my Widal test is positive?
To know if your Widal test is positive, you need to be aware of the symptoms. If you have a sore throat and cough, it may be good to get tested. The test result comes up positive only when the patient's erythrocytes can agglutinate with the bacteria in the blood sample.
4. What causes Widal test positive?
Typhoid toxin is produced in the cells of Salmonella typhi, the bacterium that causes the illness. People's immune systems create antibodies against this toxin when they consume it. This is what results in a positive Widal test. Additionally, the actively infected person has a TO antigen titer of greater than 1:160.Â
5. Why is the Widal test not recommended?
Widal testing is not recommended because it can cause the following problems:
- It is not as accurate as other tests such as FTA.
- It may give false positive and false negative results for typhoid fever.
- It takes a long time to get the results from this test, which can be a problem when an immediate diagnosis is needed.
6. When should the Widal test be done?
The Widal test should be done when there is a suspicion of typhoid fever. It can also be done when there are signs of a possible infection or when the person has been in contact with someone who has typhoid fever. It is also recommended when a person has had exposure to the bacteria and has some symptoms.
7. What is the Widal test cost in India?
The Widal test is a low-cost and reliable approach to determine whether a person has typhoid fever and/or has been exposed to germs. Depending on the city and the type of laboratory, it can cost anywhere between Rs 450 and Rs 550 on average in India.
8. How is typhoid diagnosed by a Widal test?
- The patient's serum is mixed with antigen from Salmonella typhi bacteria.
- If the patient has been infected, antibodies will bind to these antigens and form an antigen-antibody complex.
- These complexes will then be revealed by adding a specific type of dye.
9. What is the Widal test procedure?
The Widal test is a diagnostic procedure used to detect the presence of antibodies against Salmonella typhi and Salmonella paratyphi in the blood. It is a simple test that involves mixing a patient's serum with antigens derived from the two bacteria. The patient's serum is then tested for the presence of antibodies against the two antigens. If the patient has antibodies against either of the two antigens, then the test is considered positive.
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References:
Abraham, G., Teklu, B., Gedebu, M., Selassie, G. H., & Azene, G. (1981). Diagnostic value of the Widal test. Tropical and geographical medicine, 33(4), 329-333.
Aziz, T., & Haque, S. S. (2012). Role of Widal test in the diagnosis ofyphoid fever in context to other test. Am J Biochem Biotechnol, 2, 16-18.
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