USMLE Forum Archives - USMLE Step 3 - Trepenomal Vs nontreponomal tests
Trepenomal Vs nontreponomal tests
meduploader - 05-07-09 22:20
Non Treponemal Tests: VDRL, RPR
Principle: Syphilitic infection leads to the production of nonspecific antibodies that react to cardiolipin the basis of traditional non-treponemal tests such as the VDRL test and rapid plasma reagin test.
Mainly used as screening tests Sensitivity, however, is very low in Early Primary syphilis and during late syphilis during these periods, 1/3 of pts may be non reactive. So, if suspicion is very high despite a negative screening test, go ahead with treponemal specific test ( FTA-Abs)
False Positives are common in pregnancy, autoimmune diseases and infections
False negative reactions can occur too : large amounts of antibody block the antibody-antigen reaction, causing a false-negative test in the undiluted sample ( Prozone phenomenon – similar to hook effect)
Use in Monitoring treatment adequacy : In many cases nontreponemal tests become nonreactive after adequate syphilis treatment – so, use VDRL/ RPR for follow-up after treatment. However, remember that even with sufficient treatment, patients sometimes have a persistent low-level positive nontreponemal test (referred to as a serofast reaction). However, this drop in titers can help in follow up
Remember: Titers are not interchangeable between different test types. Hence, the same nontreponemal test should be used for follow-up evaluations.( If used RPR for screening, use the same for follow up)
Treponemal Tests
Treponemal-specific tests detect antibodies to antigenic components of T. pallidum.
Used primarily to confirm the diagnosis of syphilis in patients with a reactive nontreponemal test. ( So, if you have a positive RPR, the next step is FTA-Abs or TPHA)
Treponemal-specific tests : EIA for anti-treponemal IgG, the T. pallidum hemagglutination (TPHA) test, the microhemagglutination test with T. pallidum antigen, the fluorescent treponemal antibody-absorption test (FTA-abs), and the enzyme-linked immunosorbent assay.
Treponemal tests have sensitivities and specificities equal to or higher than those for nontreponemal tests. However, treponemal-specific tests are more difficult and expensive to perform, which limits their usefulness as screening tests.
False-positive results can occur, especially when the FTA-abs test is used in patients with systemic lupus erythematosus or Lyme disease.
meduploader - 05-07-09 22:20
Non Treponemal Tests: VDRL, RPR
Principle: Syphilitic infection leads to the production of nonspecific antibodies that react to cardiolipin the basis of traditional non-treponemal tests such as the VDRL test and rapid plasma reagin test.
Mainly used as screening tests Sensitivity, however, is very low in Early Primary syphilis and during late syphilis during these periods, 1/3 of pts may be non reactive. So, if suspicion is very high despite a negative screening test, go ahead with treponemal specific test ( FTA-Abs)
False Positives are common in pregnancy, autoimmune diseases and infections
False negative reactions can occur too : large amounts of antibody block the antibody-antigen reaction, causing a false-negative test in the undiluted sample ( Prozone phenomenon – similar to hook effect)
Use in Monitoring treatment adequacy : In many cases nontreponemal tests become nonreactive after adequate syphilis treatment – so, use VDRL/ RPR for follow-up after treatment. However, remember that even with sufficient treatment, patients sometimes have a persistent low-level positive nontreponemal test (referred to as a serofast reaction). However, this drop in titers can help in follow up
Remember: Titers are not interchangeable between different test types. Hence, the same nontreponemal test should be used for follow-up evaluations.( If used RPR for screening, use the same for follow up)
Treponemal Tests
Treponemal-specific tests detect antibodies to antigenic components of T. pallidum.
Used primarily to confirm the diagnosis of syphilis in patients with a reactive nontreponemal test. ( So, if you have a positive RPR, the next step is FTA-Abs or TPHA)
Treponemal-specific tests : EIA for anti-treponemal IgG, the T. pallidum hemagglutination (TPHA) test, the microhemagglutination test with T. pallidum antigen, the fluorescent treponemal antibody-absorption test (FTA-abs), and the enzyme-linked immunosorbent assay.
Treponemal tests have sensitivities and specificities equal to or higher than those for nontreponemal tests. However, treponemal-specific tests are more difficult and expensive to perform, which limits their usefulness as screening tests.
False-positive results can occur, especially when the FTA-abs test is used in patients with systemic lupus erythematosus or Lyme disease.
Page 1
Page 1