Widal Test: Understanding and Application

Widal examination Basic theory Widal examination is a serological examination which aims to confirm the diagnosis of typhoid fever. A positive Widal test means that there are anti-substances (antibodies) against Salmonella germs, indicating that a person has been in contact/infected with a certain type of Salmonella germ. This test will show the reaction of Salmonella antibodies to O-somatic and Hflagellar antigens in the blood. The widal test examination technique can be carried out using two methods, namely the wipe/roll test (test slides) and tube test (tube test). The difference is, the tube test requires an overnight incubation time because it requires a more complicated technique and the Widal launch test only requires an incubation time of 1 minute which is usually used in screening procedures. Generally, the Widal launch test is now more widely used. The sensitivity and specificity of this test are greatly influenced by the type of antigen used. According to several researchers, the Widal test which uses antigens made from germ strains originating from endemic (local) areas provides higher sensitivity and specificity than when using antigens originating from germ strains originating from outside endemic areas (import). However, according to a study that measured the ability of the Widal Tube Test using imported antigens and local antigens, there was a significant correlation between local antigens and imported S.typhi O and H antigens, so that imported antigens could be considered for use in laboratories that cannot produce antigens. itself to help confirm the diagnosis of typhoid fever.In the Widal test examination, several antigens are known that are used as parameters for assessing Widal test results. The following is an explanation of the types of antigens: f. O antigen is somatic which is located in the outer layer of the germ body. Its chemical structure consists of lipopolysaccharide. This antigen is resistant to heating at 100 °C for 2–5 hours, alcohol and dilute acids. g. The H antigen is an antigen located in the flagella, fimbriae or fili of S. typhi and has a protein chemical structure. S. typhi has a single H phase-1 antigen which is also shared by several other Salmonella. This antigen is inactive on heating above 60 °C and on administration of alcohol or acid. h. The Vi antigen is located in the outer layer of S. typhi (capsule) which protects germs from phagocytosis with the chemical structure of glycolipids. It will be damaged when heated for 1 hour at 60 °C, with the addition of acid and phenol. This antigen is used to detect the presence of a carrier. The usefulness of the Widal test for the diagnosis of typhoid fever is still controversial among experts. However, almost all experts agree that an increase in agglutinin titer of more than or equal to 4 times, especially agglutinin O or agglutinin H, has important diagnostic value for typhoid fever. A high increase in agglutinin titer in a single specimen cannot differentiate whether the infection is a new or old infection. Likewise, an increase in agglutinin titers, especially agglutinin H, does not have an important diagnostic meaning for typhoid fever, but it can still help and confirm the diagnosis of suspected typhoid fever in adult sufferers who come from non-endemic areas or in children aged less than 10 years in endemic areas, because in this group of sufferers the possibility of coming into contact with S. typhi in subinfectious doses is still very small. In adults or children over 10 years of age who live in endemic areas, the possibility of ingesting subinfectious doses of S.typhi is still greater so that the Widal test can provide a threshold for reference titers that vary between one endemic area and another. depending on the level of endemicity and also differs between children under 10 years of age and adults. Thus, if the Widal test is still needed to support the diagnosis of typhoid fever, then the upper threshold for reference titers, both in children and adults, needs to be determined. One of the very important weaknesses of using the Widal test as a means of supporting the diagnosis of typhoid fever is the rather low specificity and difficulty in interpreting the results, because many factors influence the increase in titer. In addition, antibodies to the H antigen may even be found in higher titers, which is due to extensive cross-reactivity making it difficult to interpret. For this reason, testing for H antibodies is not recommended in endemic areasS. typhi, simply check the titer for O antibodiesS. typhi. Widal titers are usually multiples of: 1/32, 1/64, 1/160, 1/320, 1/640. a)Increase in Widal test titer 4 x (over 2-3 weeks): declared (+). b)Titer 1/160: still to see in the next week whether there will be an increase in titer. If there is, it is declared (+). c)If 1 x direct examination is 1/320 or 1/640, it is immediately declared (+) in patients with typical clinical symptoms. Purpose of inspection:Detect typhus or typhoid fever. Principle : The principle of the agglutination reaction that occurs when patient serum is mixed with antigen suspensionSalmonella typhosa. A positive examination is when an agglutination reaction occurs between the antigen and antibody (agglutinin). The antigenused in the Widal test comes from salmonella suspension that has been killed and processed in the laboratory. By diluting the serum, anti levels can be determined. The highest dilution that still causes an agglutination reaction indicates the antibody titer in the serum. 1.1 Tools and reagents Tools: white slide, stirrer, micropipette Reagents:S. typhi , S. typhi H,S. paratyphi AH,S. paratyphi BH Ways of working : a. Prepare a dry and clean slide with 4 (four) circles b. With a micropipette, insert Tydal reagent with a volume of 40ul into the circles. c. Next, serum was added with a titer level of 1/80 with a sample volume of 20ul. d. Mix and shake e. If the results are (+) agglutination, continue with the next titer level, namely 1/160 and 1/320 f. Mix and shake. g. Record and report results Note: the examination should not be carried out for more than 1 minute, because if it is longer it can cause false positive results. Interpretation of results: a. High O titer: (≥160) or a high increase in titer indicates acute infection b. High H titer: (≥160) Indicates that there has been factionalization/an infection has occurred c. To obtain a titer of 1/80: Have you ever had typhoid: Normal Never had Typoid: the examination is carried out again within a certain period of time 5-7 days d. To obtain a titer of 1/160: Have experienced typhoid : the examination is carried out again within 5-7 days Never had Typhoid: (+) Typoid e. To obtain a titer of 1/160: Have experienced typhoid : (+) Typhoid Never had Typoid : (+) Typhoid