What is the Difference Between Treponemal and Nontreponemal Test?
🆚 Go to Comparative Table 🆚The difference between treponemal and nontreponemal tests lies in the type of antigen the antibodies are directed against. These tests are used to diagnose syphilis, a sexually transmitted infection caused by the bacterium Treponema pallidum.
Treponemal tests detect antibodies specific to T. pallidum proteins. Examples of treponemal tests include the microhemagglutination assay for T. pallidum, Treponema pallidum Haemagglutination Assay (TPHA), and various enzyme immunoassays. A positive treponemal test indicates a current or past infection of syphilis, but it cannot differentiate between active or previously treated infections.
Nontreponemal tests detect antibodies directed against lipoidal antigens, damaged host cells, and possibly from treponemes. The most commonly used nontreponemal tests are the Rapid Plasma Reagin (RPR) test and the Venereal Disease Reference Laboratory (VDRL) test. A positive nontreponemal test indicates active syphilis, and the titer (concentration) of the test can be used to monitor the response to therapy.
In the past, the traditional algorithm for syphilis testing involved using nontreponemal tests (e.g., RPR or VDRL) as the primary screen, followed by a confirmatory treponemal test (e.g., FTA-ABS) if the nontreponemal test was positive. However, a reverse testing algorithm has been introduced, which involves using a treponemal test (e.g., immunoassay) as the primary screen and a nontreponemal test (e.g., RPR) as a supplemental test to confirm the results.
Comparative Table: Treponemal vs Nontreponemal Test
The main differences between treponemal and nontreponemal tests for syphilis are the types of antibodies they detect and their specificity for the disease. Here is a table comparing the two tests:
| Treponemal Tests | Nontreponemal Tests |
|---|---|
| Detect antibodies directed against proteins of Treponema pallidum | Detect antibodies directed against lipoidal antigens, damaged host cells, and possibly from treponemes |
| More specific for syphilis | Less specific for syphilis, can produce false-positive results due to other infections or conditions |
| Typically used to confirm a diagnosis of syphilis | Often used as an initial screening test, followed by a treponemal test for confirmation |
| Examples include microhemagglutination assay for T. pallidum, T. pallidum particle agglutination, T. pallidum hemagglutination assay, fluorescent treponemal antibody absorbed (FTA-ABS) test, and chemoluminescence immunoassays | Examples include Rapid Plasma Reagin (RPR) test and Venereal Disease Reference Laboratory (VDRL) test |
Both treponemal and nontreponemal tests are performed in clinical laboratories by skilled technicians and are usually inexpensive. A positive nontreponemal test result indicates that you may have syphilis, and a follow-up treponemal test is required to confirm a positive diagnosis.
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