Widal Test Booking, Procedureand Results [2022-23]Dr. PravalikaLast Updated on 25th November 2021
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What is the Widal Test used for?
Widal test is one of the diagnostic tests used for making a presumptive diagnosis of enteric fever/typhoid fever. Especially in developing countries or in countries where enteric fever is endemic or if resources are lacking Widal test is used as it is simple, easy to perform and less expensive. It is considered a reliable test in places where resources to perform culture tests are limited.
Widal test is used to diagnose both typhoid and paratyphoid fevers caused by Salmonella typhi and Salmonella paratyphi respectively.
What is included in a Widal Test?
The Widal test aids in the diagnosis of typhoid fever. This test utilises a suspension of killed Salmonella typhi as antigen and detects the presence of antibodies against S. Typhi in serum of patients who present with suspected febrile illness. Salmonella Typhi has two antigens – O and H. Antibodies against O are usually detected 6-8 days after onset of fever and antibodies against H antigen are usually detected 10-12 days after onset of fever. A positive result is indicated by demonstration of a four-fold or more increase in antibody titre in serum samples taken 7-10 days apart during acute and convalescent phases of infection respectively.
What is the Widal Test Procedure?
Widal test can be done in 3 ways:
- Slide test
- Semi-Quantitative Method
- Standard Tube test Method.
How to prepare for the Widal Test?
|Before test||During test|
|It is not mandatory to fast for 8-10 hours before the test.||There might be slight pain and bruising on the arm from where the blood is collected. However, these symptoms will go away quickly.|
Things to consider after the Widal Test is completed
Widal test is widely used as it is easy to perform and affordable. But false-positive results can be expected in certain situations like those who had past typhoid infection or vaccinated against typhoid. False-negative results can be seen in the early stages of illness. Hence, if the titres are found to be significantly rising by 4-fold on two occasions then the positive diagnosis of typhoid is concluded. In case if titres are not significant or inconclusive additional tests like Typhidot or blood/stool/urine/bone marrow culture are ordered by the doctors based on the symptoms.
What type of infections can a Widal Test detect?
Widal test aids in the diagnosis of both Typhoid and Paratyphoid fever caused by Salmonella typhi and Salmonella paratyphi respectively. But False-positive results are seen in certain cases like Typhus, Acute Malaria, Rheumatoid arthritis, chronic liver disease etc. Also, False-negative results are seen in the early stages of infection. Hence negative test result does not necessarily rule out the absence of infection and repeat tests might be needed to check for rising titres.
How long does it take to get Widal Test results?
Once the test samples are collected, it is sent to the lab of your choice for further testing. After the testing is completed, the Widal test results will be available on the app for downloading within the next 24-48 hours.
Is the Widal Test a definitive test?
No. As Widal test results can be either false negative in the early stages of infection or false positive for various reasons, a single test cannot be used as a definitive test. Only rising antibody titres of 4-fold or more between two widal tests done 7-10 days apart is diagnostic. Blood or bone marrow culture are considered definitive diagnostic tests for typhoid fever.
How to read the Widal test Blood test report?
A single positive Widal test is not considered diagnostic. A serum sample that shows an antibody titre of more than 1:80 for “O” and more than 1:160 for “H” antigen is considered as significant and suggestive of typhoid fever. But a single Widal test is not reliable as baseline titres in the labs can differ in different places. Hence a 4-fold or more rise in titres between samples taken 7-10 days apart is considered to be definitive evidence of typhoid infection.
Where to get the Widal Test done?
You can avail Widal test through MFine. All our lab partners are NABL (National Accreditation Board of Testing and Calibration of Laboratories) accredited labs. Thyrocare, Prima Diagnostics, Neuberg, Healthians are to name a few of our top lab partners. Most of our lab partners have the state of the art infrastructure facilities.
What affects the Widal Test results?
The Widal test has significant limitations in its specificity, sensitivity and reliability. The test results change with the course of infection.
A false-negative Widal test is more likely in the initial stages of infection or seen in cases where antibody responses in the body are diminished by early microbial treatment or in cases of typhoid relapse. Severe hypoproteinemia can cause decreased titres of antibodies against O and H antigens leading to false-negative results.
A False positive Widal test is seen in cases of the previous infection of typhoid or previous vaccination against typhoid. Widal test shows cross-reactivity with other species of Salmonella bacteria. False-positive results are also seen in cases of Acute Falciparum Malaria (especially in children), Rheumatoid Arthritis, Nephrotic syndrome, Chronic liver disease with low globulin levels.
Widal test needs a reference baseline titres from a healthy local population and this differs from time to time and place to place making it difficult to have a standard cutoff level.
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Frequently Asked Questions
What are Antibodies?
Antibodies, also known as immunoglobulins, are protective proteins generated in the body when exposed to Antigens. Antibodies are used by the immune system to detect and destroy foreign objects like bacteria, viruses etc., Bacteria, Viruses or such foreign objects are the Antigens. Antibodies are proteins that identify the antigens and adhere to them in order to eliminate foreign objects from the body.
Salmonella typhi causes typhoid fever, a bacterial infection that grows in the intestine and blood. Salmonella bacteria possess O antigen and H antigen. Salmonella Paratyphi bacteria possess O, AH and BH antigens. Antibodies against Salmonella typhi O and H antigens or against Salmonella paratyphi AH and BH antigens are produced by the patient’s body after infection with S. Typhi or S. Paratyphi bacteria respectively.
Why is this test performed?
Widal test is used to see if there are any antibodies developed against Salmonella species in the blood. It aids in the diagnosis of Enteric fever or Typhoid or Paratyphoid fever caused by Salmonella typhi and Salmonella paratyphi A, B, and C. If you have symptoms like fever, weakness, severe headache, lack of appetite, rose-coloured patches on the trunk, discomfort in the abdomen/stomach pain, chills, nausea or vomiting, constipation or diarrhoea, muscle weakness, your doctor may recommend this test. This test may be advised for patients receiving treatment for typhoid or paratyphoid fever to determine how effective the ongoing treatment is.
What are the Precautions for the Widal test?
Some drugs can affect the Widal test findings, you should tell your doctor about all of your current medications before the test. Also, let your doctor know if you had a past history of Enteric fever or vaccination against Typhoid infection.
What are the Preparations for the Widal Test?
Can we avail Widal Test at Home?
Yes. Widal test requires a blood sample that can be collected at your doorstep. The collected sample is then sent to the lab to perform the test.
What happens once the Widal Test results are available?
If the test results are negative, it may indicate that there is no infection caused by Salmonella species. But the result can be negative in the early stages of infection. Hence, the Doctor might ask you to repeat the Widal test after 7-10 days if you continue to show symptoms related to Typhoid fever. In case the test results are positive, it may indicate that there may be a chance for infection caused by Salmonella species and you may consult with your doctor. The doctor will correlate your symptoms, past medical history and test reports and then start your treatment.
|UNISEX||All age groups||Agglutination is seen in positive cases|
What are Widal Test Normal Readings?
An antibody titre of more than 1:80 for O antigen and more than 1:160 for H antigen is suggestive of enteric fever. Antibody titres lower than this are common in healthy individuals. A single positive test is not significant due to its limitations.
A 4-fold or more rise in titres between two samples taken 7-10 days apart is considered as definitive evidence of typhoid infection.
What is the typhoid positive ratio?
Based on the concentration and ratio of antigen and antibody, agglutination is seen in the Widal test. The highest dilution of serum sample of the patient that shows visible agglutination is considered as the titre of the patient. An antibody titre of more than 1:80 for O antigen and more than 1:160 for H antigen is considered positive.
What happens once I get my Widal test results?
Based on your symptoms you might have been started on empirical treatment by your doctor if typhoid is common in your locality or city or if your doctor has strong suspicion for typhoid infection to prevent complications.
Once your test results are received if the test is positive you will be given typhoid specific treatment.
If the test is inconclusive either the Widal test is repeated to see the titres or Typhidot or blood culture/ other tests are performed.
If the Widal test is negative and typhoid fever is excluded from diagnosis then other tests are performed to see for the presence of other infections.