Purpose serological test for enteric fever In and named after its inventor, Georges-Fernand Widal , is a presumptive serological test for enteric fever or undulant fever whereby bacteria causing typhoid fever is mixed with a serum containing specific antibodies obtained from an infected individual. In cases of Salmonella infection, it is a demonstration of the presence of O-soma false-positive result. Test results need to be interpreted carefully to account for any history of enteric fever, typhoid vaccination, and the general level of antibodies in the populations in endemic areas of the world. Typhidot is the other test used to ascertain the diagnosis of typhoid fever. As with all serological tests, the rise in antibody levels needed to perform the diagnosis takes 7—14 days, which limits its applicability in early diagnosis. Other means of diagnosing Salmonella typhi and paratyphi include cultures of blood, urine and faeces.
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Sponsored link The Widal test is a test procedure that involves mixing of the bacteria which cause typhoid fever to the blood consisting of certain antibodies taken from an infected person. It is an assumptive serological test used for undulant fever or enteric fever. When the Widal test is used to check of the presence of Salmonella infections, then it is a presentation of the occurrence of O-soma false-positive result. It is important to carefully and correctly interpret the test results as per the past history of enteric fever, the typical composition of antibodies in the general population living in the endemic regions of the world and typhoid vaccination.
Another test which is employed to detect and diagnose typhoid fever is the Typhidot test. The other procedures that can be used to diagnose Salmonella typhi or paratyphi include options like urine, blood and stool cultures.
It may be noted that such microbes make H2S from thiosulfate which can be effortlessly recognized on differential media like Bismuth sulfite agar. Occasionally 2-mercaptoethanol is combined to the Widal test. This chemical has the ability to easily denture the IgM class of antibodies.
Thus when a reduction in the tier is observed after utilizing this agent, then it indicates that the input of IgM has been eliminated with the IgG constituent left behind.
This distinguishing of antibody classes is vital, as it permits for the differentiation of a recent infection IgM from an older infection IgG. The Widal test result is positive: If the TO antigen titre is greater than in an infection that is active, OR If TH antigen titre is greater than in older infection or in immunized individuals A single Widal test holds little clinical applicability due to the several cross reacting infections, which include malaria.
Sponsored link The Widal test can be conducted via the two below listed methods: Tube agglutination Slide Agglutination It may be noted that tube agglutination has more accuracy as compared to the slide agglutination technique. It is possible to go up to titres in the tube agglutination method, whereas the slide method limits the test to titres only.
However, the slide agglutination is faster with the results being produced inside five minutes. The Widal test procedure is carried out in the following way: Prepare a sequence of serum dilutions for every antigen that is to be tested. Take tubes with 0. Dry and thoroughly cleansed test tubes have to be used.
Make dilutions starting with and doubling-up through Mix 0. Make a series of ten dilutions that end with so as to detect possible increase in titre in the submitted sample. In simple words, the procedure involves: Preparation of the blood plate with black background Addition of a single drop of serum Addition of antigens, i. Hence a Widal test performed early in the first week may give negative results.
A single Widal test is not sufficient for correct results and at least two tests should be conducted. The level of antibodies of a population in a given area indicates the baseline titre. One has to know this before interpreting a Widal test. O antigen with a titre of or more and H antigen with a titre of or more are deemed important Patients who have already undergone antibiotic treatment may not show any increase in titre on a Widal test. Patients vaccinated against Salmonella may show false positive reactions which can be verified with another Widal test in the next week.
Then vaccinated people will not show any increase in titre, while untreated cases will show rise in titre in the Widal test results Patients with past history of enteric fever may have Salmonella antibodies and hence may show false negative reactions. This can be verified with a second test in the next week, which shows rise in titre. Sponsored link.
Widal test: Principle, Procedure, Results, Interpretation, Significance and Limitation
Widal test card or slide. Procedure of Widal Test Widal test can be done in two ways. One is rapid test on slide and another is tube test in which result may be obtained after one night of incubation. For Rapid Slide Test Clean the glass slide or test card supplied in the kit well and make it dry. Place a drop of undiluted test serum in each of the four labelled circle 1, 2, 3 and 4 ie O, H, AH and BH and place a drop of Negative control serum in circle 5 and Positive control in circle 6.
Widal Test- Introduction, Principle, Procedure, Interpretation and Limitation
Laboratory diagnosis of enteric fever includes Blood culture, Stool Culture and Serological test. Widal test is a common agglutination test employed in the serological diagnosis of enteric fever. Antibodies in serum, produced in response to exposure to Salmonella organisms will agglutinate bacterial suspension which carries homologous antigens. This forms the basis of Widal test. The organisms causing enteric fever possesses two major antigens namely somatic antigen O and a flagellar antigen H along with another surface antigen, Vi. During infection with typhoid or paratyphoid bacilli, antibodies against flagellar antigen of S. Positive result is indicated by the presence of agglutination Absence of agglutination indicates a negative result.