![]() To discriminate between a falsely reactive screening result and past syphilis, a second treponemal-specific antibody test is recommended using a method that is different from the initial screen test (eg, TP-PA). In some patients, the results of the treponemal screening test and RPR may be discordant (eg, syphilis IgG positive and RPR negative). Therefore, the results of a nontreponemal assay, such as RPR, are needed to provide information on a patient's disease state and history of therapy.(Table) This is because treponemal tests may remain reactive for life, even following adequate therapy. A positive treponemal test suggests infection with T pallidum but does not distinguish between recent, past, treated, or untreated infections. Syphilis screening at Mayo Clinic is performed using the reverse algorithm, which first tests sera for T pallidum specific IgG antibodies using an automated enzyme immunoassay. Alternatively, if the TP-PA is negative, the initial positive screen is interpreted as a false-positive result. If the TP-PA is positive, this would indicate previously treated or late-stage syphilis infection. If the RPR is negative, the sample is reflexed to a second treponemal assay, such as the T pallidum particle agglutination (TP-PA) assay. If this screening assay is positive, the sample is reflexed for testing by RPR, which, if positive, is reported with a titer and is indicative of active or recent syphilis infection. This algorithm starts with an automated treponemal assay to detect antibodies specific to T pallidum. Although the FTA-ABS and MHA-TP assays are technically simple to perform, they are labor intensive and require subjective interpretation by testing personnel.Īs an alternative to the traditional syphilis screening algorithm, many laboratories utilize the reverse syphilis screening algorithm. Therefore, a positive result by RPR or VDRL requires confirmation by a treponemal-specific test, such as the fluorescent treponemal antibody-absorption (FTA-ABS) or microhemagglutination (MHA-TP) assay. Because these tests measure the host's immune response to nontreponemal antigens, they lack specificity. Historically, the serologic testing algorithm for syphilis included an initial nontreponemal screening test, such as the rapid plasma reagin (RPR) or the VDRL tests. ![]() ![]() These features, together with the fact that T pallidum cannot be isolated in culture, mean that serologic techniques play a major role in the diagnosis and follow-up of treatment for syphilis. The infection is systemic, and the disease is characterized by periods of latency. VersAddendum to the Instruction Manual 2.Syphilis is caused by infection with the spirochete Treponema pallidum subspecies pallidum. The distribution of intensity of the scattered light depends on the ratio of the particle size of the antigen-antibody complexes to the radiated wavelength.(Instruction manual: Siemens Nephelometer II, Siemens, Inc. The result is calculated by subtracting the value of the final measurement from the initial measurement. An antigen-antibody complex is formed in the final measurement. Antigen and antibody are mixed in the initial measurement, but no complex is formed yet. The light is scattered onto the immuno-complexes that are present. A light beam is generated with a light emitting diode, which is transmitted through the cuvette. ![]() Antigen-antibody complexes are formed when a sample containing antigen and the corresponding antiserum are put into a cuvette. If the antibody volume is kept constant, the signal behaves proportionally to the antigen volume.Ī reference curve is generated by a standard with a known antigen content on which the scattered light signals of the samples can be evaluated and calculated as an antigen concentration. The intensity of the measured scattered light is proportional to the amount of antigen-antibody complexes in the sample under certain conditions. In this Siemens Nephelometer II method, the light scattered onto the antigen-antibody complexes is measured. In: Rifai N, Chiu RWK, Young I, Burnham CAD, eds. Dietzen DJ, Willrich MAV: Amino acids, peptides, and proteins. Kyle RA: Detection of quantitation of monoclonal proteins. In: Middleton Jr E, Reed CE, Ellis EF, et al, eds. Ballow M, O'Neil KM: Approach to the patient with recurrent infections. Kyle RA, Greipp PR: The laboratory investigation of monoclonal gammopathies. Dispenzieri A, Gertz MA, Kyle RA: Distribution of diseases associated with moderate polyclonal gammopathy in patients seen at Mayo Clinic during 1991. Pinching AJ: Laboratory investigation of secondary immunodeficiency. Webster ADB: Laboratory investigation of primary deficiency of the lymphoid system.
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