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Serologic Testing for Syphilis


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Diagnosis: Laboratory Testing

Slide 4

April 2011

There are a number of different laboratory methods that have been developed to assist in the diagnosis of syphilis, but many of these tests are not routinely used in the clinical laboratory. The rabbit infectivity test, or RIT assay, demonstrates high sensitivity and specificity for the detection of Treponema pallidum. However, this method is time-consuming and laborious and is limited to research settings. A second method is dark- field microscopy, which allows for the visualization of the spirochete in clinical samples as you can see in the image on this slide. Dark-field microscopy possesses relatively high specificity, but this method is not routinely performed in many clinical labs due to the low prevalence of positive samples. Similarly, microscopy following immunostaining, such as direct fluorescent antibody or silver staining, can be applied to tissue samples. But this method is also uncommon in clinical labs. Polymerase chain reaction, or PCR, is a technology that offers a lot of promise for improving the laboratory diagnosis of syphilis. Several studies have shown that PCR may allow for a rapid and sensitive detection of Treponema pallidum in clinical samples; however, there are currently no commercially-available PCR assays, and this technology is not widely available in clinical laboratories.

Diagnosis: Laboratory Testing


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