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The Widal Test: A Brief Overview, Concept, and Method
Our website offers a range of services The Widal test is a serological blood test used to determine whether the body has typhoid or enteric fever. The initial administration of this examination took place in 1896 under the supervision of Georges Ferdinand Widal, who subsequently had the test named after him.
The Widal test employs a sophisticated method to identify antibodies the body produces against the Salmonella bacterium that causes typhoid fever. id fever. This test detects the presence of O and H antibodies in a patient’s blood sample (serum).
The purpose of this test is to detect life-threatening illnesses like typhoid fever. Nevertheless, it is crucial to accurately interpret the Widal test in order to obtain accurate results.
Continue reading this blog to comprehend the significance of the Widal test, its underlying principle, the steps involved in the method, and the interpretation of the test results.
Typhoid fever and the Widal test
The Salmonella bacterium causes typhoid fever, also known as enteric fever, a highly serious disease. This bacterium affects your gastrointestinal tract when you consume food or drink that contains fecal matter.alfecal matter.
An individual afflicted with typhoid fever would manifest symptoms such as exhaustion, elevated body temperature, migraines, gastrointestinal disturbances, including diarrhea or constipation, abdominal discomfort, loss of body mass, and the appearance of red patchesEarly detection and prompt treatment of typhoid fever are crucial in reducing the risk of developing serious complications such as profound intestinal hemorrhage or perforation.agehemorrhage or perforation.
Several diagnostic techniques, including stool culture and bone marrow analysis, can be used to detect typhoid fever. The Widal test, for example, identifies the presence of antibodies produced by your body in response to salmonella bacteria during typhoid fever.
The etiological agent responsible for typhoid fever is the Salmonella bacterium. Person-to-person contact or contaminated food can transmit the disease. There are two types of bacteria:
Alternatively known as S. Typhi, Salmonella Typhi,
Salmonella Paratyphi, also known as S. Paratyphi, is a bacteria.
The bacterium S. Typhi is known to possess two antigens:
The primary antigen of S. Typhi O (TO) is
The secondary antigen belongs to S. Typhi H (TH).
In contrast, the bacterium S. paratyphiparatyphi possesses the following two antigens:
S. paratyphiparatyphi A refers to Salmonella paratyphiparatyphi A, a specific strain of the Salmonella bacteria.
S. Paratyphi B
In order to comprehend and analyzeanalyze the Widal test reports, we will thereafter examine these values in this blog for the purpose of understanding and interpreting the Widal test findings.
The Widal Test is based on the principle of detecting antibodies in the blood that are specific to certain bacteria causing typhoid fever.
When you ingest contaminated food, the Salmonella bacterium enters your body as an antigen. ith it. Once the antigens enter your digestive system, your immune system produces antibodies to fight against them. Consequently, antigens clump together (react), indicating the presence of typhoid disease.
This agglutination test identifies the antibodies produced by your body in response to a certain microbe or antigen. If you contract typhoid fever, the antibodies in your blood will react, causing salmonella antigens to clump in an agglutination test.
The Widal test’s fundamental idea is that the presence of a specific antibody in the serum will result in a visible clumping reaction with a corresponding antigen on the test card.
The next phase of this investigation quantifies the concentration of the affirmative antigen, known as the titre.
Procedure for Widal Test Preparation
Widal Test for Slide
In order to prepare for a Widal test, the following items are necessary:
- Serum from the patient
- A pipette is a laboratory tool for measuring and transferring small volumes of liquid precisely and accurately.
- The fluid component of blood remains after clotting has occurred.
- The S. antigenantigen consists of four types: O, H, AH, and BH.
- Slip
- Blend Rod
- Chronometer
In addition, it is necessary to have reagents for the identification of antigens such as O Ag (somatic or surface antigen), H Ag (flagella antigen), AH Ag, BH Ag, and so on.
The Widal test follows a two-step protocol:
- Widal Test for qualitative analysis
- The test will require the use of a slide with six reaction circles, each labeled O, H, AH, BH, PC, and NC. PC, and NC. First and foremost,
- Place a single droplet of the patient’s serum in each of the four reaction circles, specifically labeledlabeled as O, H, AH, and BH.
- Put one droplet of positive control in the PC designated area and another droplet in the NC designated area.
- Subsequently, place a single droplet of O antigen within the O circle, P antigen within the P circle, AH antigen within the AH circle, and BH antigen within the BH circle, respectively.
Include any antigen, such as O, H, AH, BH, in both positive control (PC) and negative control (NC).
Subsequently, thoroughly combine the serum and antigen within each circle to prevent the combination from exceeding the boundaries of the circle and coming into contact with the slide.
Furthermore, it is imperative to avoid mixing different mixtures, as this can significantly impact the accuracy of the test findings.
Lastly, gently spin the slide in a deliberate circular motion to ensure a thorough blending of the serum and reagent.
Upon completion of all tasks, the outcomes will become visible. If the test yields a positive result, it will resemble the PC (positive control) circle, and if it yields a negative result, it will resemble the NC (negative control) circle. To put it simply, the presence of agglutination will yield positive test findings, and conversely, the absence of agglutination will yield negative results.
If the test findings are positive, the subsequent stage will entail a quantitative test. In order to confirm the diagnosis of typhoid fever, we shall conduct a test using the antigen reagent that yields a positive result. For example, if the qualitative test yields a positive result for O, we will use the O reagent in the quantitative test.
Typically, S. typhi-specific O and H antigens confirm the diagnosis. Only a small number of individuals test positive for AH or BH during a qualitative test.
The Widal test is a quantitative semi-procedure that involves checking for the presence of O antigen if O is positive, H antigen if H is positive, and both antigens if both are positive. To execute this examination, adhere to the following instructions:
Use an alternative slide containing a total of eight circles, with four circles designated for the O antibody and four circles designated for the H antibody.
If the O result was positive in the previous test, place 5 microliters of the patient’s serum in the first O circle, 10 microliters in the second circle, 20 microliters in the third circle, and 40 microliters in the fourth circle, horizontally.
Similarly, place a single droplet of the designated reagent in each of the four rings.
To submit, indicate the values from the right side. Place the mark 1:40 on the fourth circle, the mark 1:80 on the third circle, the mark 1:160 on the second circle, and the mark 1:320 on the first circle.
This paper aims to explain the Widal Test using the Slide Method.
After thoroughly mixing the serum and reagent and rotating the slide, patiently wait for the results to appear. If the O circle registers a value greater than 100 and the H circle registers a value greater than 200, we will consider the outcome positive.
Put simply, a Widal test is considered positive if the titre exceeds 100 for O antigen and 200 for H antigen. However, the outcomes may be adverse as a result of antibiotics, malaria, dengue, or if the fever persists for an extended period of time.
There are several methods in which you might analyze and understand your test results:
If the concentration of S. Typhi is less than or equal to 1:80, the result is negative. If the concentration is greater than or equal to 1:160, the result is positive.
If the concentration of S. paratyphi is less than or equal to 1:80, the result is negative, and if it is greater than or equal to 1:160, the result is positive.
A positive S. typhi O test indicates that there is an ongoing fever. However, if S. Typhi H is positive, the fever indicates a previous infection. Furthermore, the Widal test is considered within the normal range if the titre is 1:80 or lower for both O and H antigens.
Widal Test for Tuberculosis
In addition to the qualitative and quantitative Widal tests, there is an alternative testing method known as the standard tube method. In this method, we collect a total of eight tubes, dilute them, and then observe them. The initial test has the capability to detect typhoid fever; nevertheless, a tube Widal test is required to definitively confirm the presence of the disease.
Initially, the detection of typhoid fever used two types of tubes:
For H agglutination, use the Dreyer’s tube.
The O agglutination process uses a Felix tube.
We currently use three Kahn tubes, each containing 0.5 ml, for the agglutination of both O and H.
The Standard Tube Method follows this procedure:
In order to do a Widal test, the following items are necessary:
The patient’s serum was collected.
The antigens O, H, AH, and BH are present.
Isotonic saline solution
A pipette is a precise laboratory tool for measuring and transferring small volumes of liquid.
Laboratory apparatus used for holding and organizing test tubes.
Test tubes
A water bath is a container filled with water that is used to heat or cool substances in a controlled manner.
Before we begin this examination, we must recognize that the tube method is a dilution procedure that requires precise execution. Let’s comprehend this examination using more straightforward terminology.
Begin by taking nine tubes and putting them in the rack. For the letter O, label the tubes sequentially with numbers ranging from 1 to 9.
Combine and blend 0.1 ml of normal saline with 0.9 ml of serum in the initial test tube. Alternatively, introduce 0.5 normal saline solution into each of the remaining tubes.
Subsequently, extract 0.5 ml from the initial tube and introduce it into the second tube. Test tube 1 will have 0.5 ml of the leftover solution, whereas test tube 2 will contain 1 ml.
Repeat this procedure, extracting 0.5 ml from the previous tube and introducing it into the subsequent tube, resulting in a total volume of 1 ml. Using the 8th tube, extract 0.5 ml and transfer it to a separate tube.
Thoroughly blend all of the tubes. The tubes will undergo a primary serial dilution, with dilution ratios of 1:10, 1:20, 1:40, 1:80, 1:160, 1:320, 1:640, and 1:1280 for the 1st to 8th tubes, respectively.
Obtain a fresh test tube, namely the ninth one in the series, and introduce the positive control substance.
Next, add 0.5 ml of the corresponding antigen (O, H, AH, BH) to each of the eight tubes. This will result in a final volume of 1 ml for each tube.
When a reagent is added to each of the tubes, the resulting serial dilution of the tubes, ranging from the 1st to the 8th, will be as follows: 1:20, 1:40, 1:80, 1:160, 1:320, 1:640, 1:1280, and 1:2580.
Thoroughly combine the ingredients, then place a cover on the tubes and keep them at a temperature of 37°C for the duration of one night (about 18 to 24 hours).
Explanation of the Widal Test-Tube Method
If you have typhoid fever and experience agglutination, you will notice that the 9th tube, which is the positive control, will resemble one of the other eight tubes. In the absence of enteric fever, the normal range of the eight tubes and widal test will remain unchanged.
When the tube displaying agglutination has a titre greater than 1:100 for O and 1:200 for H, a positive Widal test indicates an active infection. Furthermore, we consider all other titers to be within the standard range for a Widal test.
The Widal Test has limitations
The widal test is undoubtedly a rapid and efficient method for diagnosing typhoid fever, but it does have several drawbacks, such as:
Falsely positive results in the Widal test might occur due to prior immunization or infection with S. typhi.
The Widal test is a lengthy procedure, and by the time a diagnosis is reached, it may be too late to initiate therapy.
The Widal test is unable to differentiate between a patient’s previous infection, ongoing illness, or vaccination against S. Typhi.
Positive test findings for typhus, acute falciparum malaria, chronic liver illness, rheumatoid arthritis, nephrotic syndrome, and myelomatosis can be misleading or inaccurate.
Due to the multitude of variables that can impact the test outcomes, it is advisable not to rely solely on this test for diagnosing typhoid.
However, for screening purposes, it is usually advisable to select reputable laboratories. An interruption or inefficient examination process can result in therapy being postponed.
Cost of Widal Test
The Widal test is a rapid and cost-effective diagnostic test primarily employed in underdeveloped nations with a high incidence of typhoid fever. The cost of the widal test can vary depending on the geographical region, laboratory center, and other factors. Metropolis Labs prices the wide test at xxxx.
hat enable you to conveniently monitor the progress of your sample, access and download reports, schedule a home visit, and upload prescriptions. To schedule a Widal test and receive prompt results, contact Metropolis Labs today.
In conclusion,
The Widal test is a rapid diagnostic method used to identify cases of typhoid fever or enteric fever. Detecting this fever requires only a patient’s serum and a few reagents. Nevertheless, due to the potential impact of many circumstances on the test outcomes, it is advisable to conduct this test precisely one week after the infection while adhering to the appropriate guidelines.
