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Types of Syphilis Serology Tests

Submitted on March 27, 2012

Syphilis, as most of us know, is a sexually transmitted disease. However, this disease if untreated has the potential to cause fatal damages to any part of the anatomy. Syphilis also makes a person vulnerable to other STDs like gonorrhea and HIV.

Secondly, syphilis comes with the complication of accurate diagnosis. In many cases the chancres (sores) on the skin go unnoticed or are mistaken for some other type of infection. Also, the lesions produced because of syphilis are very similar to those that develop because of other genital infections and it doesn't help that other symptoms like rashes in the palms and soles, fever, are similar to numerous other infections.

Therefore, to be on the safe side it's best to take some tests for syphilis. There are several tests a person can take, one of them being a dark field microscopy. This involves testing a scraping of the chancre or rash.

Serological Testing For Syphilis

Then there are serological tests. These tests are considered to be more reliable. Of course, the type of serological test for syphilis that is administered depends upon the stage of the disease.

Serological testing for syphilis for syphilis can be classified into two categories—treponemal and non treponemal. As the name suggests, the treponemal tests are aimed at detecting an antigen or an antibody of the T.pallidum bacteria (This is the bacteria that causes syphilis). However, a positive treponemal test cannot necessarily be indicative of an active syphilis infection. This is because antibodies remain in the bloodstream even after several years since contraction of syphilis. Non-treponemal tests on the other hand, looks for indirect indications of the infection, like the presence of cardiolipins. This is released when a treponeme bacteria damages cells. So, if cardiolipin is found in the blood sample, it indicates an active infection. However, one then needs to take a treponemal test to confirm that increased cardiolipin is in fact a result of a syphilis infection.

Non-treponemal Serologic Tests

Non-treponemal serologic tests for syphilis include VDRL (Venereal Disease Research Laboratory) test and RPR (Rapid Plasma Reagin) test. VDRL has been in use for several years now and the only difference between VDRL and RPR is that the latter does not need a microscope for result interpretation.

Treponemal Tests

Treponemal tests include FTA-ABS (Fluorescent treponemal antibody absorption) test, TPHA and MHA-TP (Treponema pallidum hemagglutination assay) and the TP-PA test (Treponema pallidum particle agglutination assay). An addition to these is rapid tests. These are lateral flow tests and use T. pallidum recombinant antigens to detect treponeme specific antibodies. Also these serologic tests for syphilis are designed to identify all T. pallidum antibody isotypes. This means that a syphilis infection can be detected as early as within a few days of exposure.

Procedure To Conduct the Tests

These tests take anywhere between two minutes to a half hour and do not require a microscope or any such laboratory equipment. The results can easily be interpreted with naked eye examination.

However, like all treponemal tests, this one too will yield a positive result for anyone who has had a syphilis infection in the past. For confirmation of an active infection, a person needs to take either an RPR or VDRL test.

Bottom-line, both types of serologic tests for syphilis are equally important in screening and diagnosing syphilis. Ideally, a person can use a non-treponemal test like VDRL or RPR for screening purposes and then take a non-treponemal test to confirm an active syphilis infection