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- Common serologic tests used routinely include:
- Sensitivity of serologic tests vary with the disease stage.
- 78-86% sensitivity for primary syphilis
- 100% sensitivity for secondary syphilis
- 95-98% sensitivity for tertiary syphilis
- Specificity is aprroximately 85-99%
- False positives on the rapid tests can be seen in viral infections (Epstein-Barr, hepatitis, varicella, measles), lymphoma, tuberculosis, malaria, endocarditis, connective tissue disease, pregnancy, intravenous drug abuse, or contamination. As a result, these two screening tests should always be followed up by a more specific treponemal test.
- Nontreponemal test antibody titers may correlate with disease activity, and results should be reported quantitatively.
- A fourfold change in titer, equivalent to a change of two dilutions (e.g., from 1:16 to 1:4 or from 1:8 to 1:32), is considered necessary to demonstrate a clinically significant difference between two nontreponemal test results that were obtained using the same serologic test.
- Sequential serologic tests in individual patients should be performed using the same testing method (e.g., VDRL or RPR), preferably by the same laboratory.
- The VDRL and RPR are equally valid assays, but quantitative results from the two tests cannot be compared directly because RPR titers frequently are slightly higher than VDRL titers.
- Nontreponemal test titers usually decline after treatment and might become nonreactive with time; however, in some persons, nontreponemal antibodies can persist for a long period of time: a response referred to as the serofast reaction.
- Most patients who have reactive treponemal tests will have reactive tests for the remainder of their lives, regardless of treatment or disease activity. However, 15%-25% of patients treated during the primary stage revert to being serologically non-reactive after 2-3 years.[1]
- Treponemal test antibody titers should not be used to assess treatment response.
- Some clinical laboratories and blood banks have begun to screen samples using treponemal tests, typically by ELISA[2] or chemiluminescence immunoassays.[1] This strategy will identify both persons with previous treatment for syphilis and persons with untreated or incompletely treated syphilis. The positive predictive value for syphilis associated with a treponemal screening test result might be lower among populations with a low prevalence of syphilis.
- Persons with a positive treponemal screening test should have a standard non-treponemal test with titer performed reflexively by the laboratory to guide patient management decisions.
- If the non-treponemal test is negative, then the laboratory should perform a different treponemal test (preferably one based on different antigens than the original test) to confirm the results of the initial test.
- If a second treponemal test is positive, persons with a history of previous treatment will require no further management unless sexual history suggests likelihood of re-exposure. Those without a history of treatment for syphilis should be offered treatment. Unless history or results of a physical examination suggest a recent infection, previously untreated persons should be treated for late latent syphilis.
- If the second treponemal test is negative, further evaluation or treatment is not indicated.
Serologic test: HIV-infected persons[edit | edit source]
- For most HIV-infected persons, serologic tests are accurate and reliable for the diagnosis of syphilis and for following a patient's response to treatment.
- However, atypical syphilis serologic test results (i.e., unusually high, unusually low, or fluctuating titers) can occur in HIV-infected persons.
When serologic tests do not correspond with clinical findings suggestive of early syphilis, use of other tests (e.g., biopsy and darkfield microscopy) should be considered.
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