Syphilis laboratory findings

Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]Associate Editor(s)-in-Chief: Aysha Anwar, M.B.B.S[2]; Nate Michalak, B.A.

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Overview

Laboratory tests which may help diagnose syphilis include darkfield examinations and tests to detect T. pallidum in lesion exudate or tissue, PCR, nontreponemal (e.g., venereal disease research laboratory (VDRL) and rapid plasma reagent test) and treponemal tests (e.g., fluorescent treponemal antibody absorbed (FTA-ABS) tests, the T. pallidum passive particle agglutination (TP-PA) assay, various enzyme immunoassays, and chemiluminescence immunoassays).

Laboratory Findings

Laboratory tests which may help diagnose syphilis include the following:

• Darkfield examinations and tests to detect T. pallidum in lesion exudate or tissue are the definitive methods for diagnosing early syphilis.

• Although no T. pallidum detection tests are commercially available, some laboratories provide locally developed PCR tests for the detection of T. pallidum.

• A presumptive diagnosis of syphilis is possible with the use of two types of serologic tests:

• Nontreponemal tests (e.g., venereal disease research laboratory (VDRL) and rapid plasma reagent test) and
• Treponemal tests (e.g., fluorescent treponemal antibody absorbed (FTA-ABS) tests, the T. pallidum passive particle agglutination (TP-PA) assay, various enzyme immunoassays, and chemiluminescence immunoassays).

• The use of only one type of serologic test is insufficient for diagnosis because each type of test has limitations, including the possibility of false-positive test results in persons without syphilis.

• False-positive nontreponemal test results can be associated with various medical conditions unrelated to syphilis, including autoimmune conditions, older age, and injection-drug use. Therefore, persons with a reactive nontreponemal test should receive a treponemal test to confirm the diagnosis of syphilis.

Nontreponemal test

• Includes VDRL and RPR tests
• Antibody titers may correlate with disease activity
• May reverse following treatment
• Used to follow treatment response
• A fourfold change in titer is necessary to demonstrate significant difference between two nontreponemal tests
• Results from two tests cannot be compared directly with each other

Trepenomal tests

• Include fluorescent treponemal antibody absorbed (FTA-ABS) tests, T. pallidum passive particle agglutination (TP-PA) assay, enzyme immunoassays, and chemiluminescence immunoassays
• Antibody titers, once positive, remain positive for the rest of the patient's life, regardless of treatment or disease activity
• Cannot be used for monitoring treatment response
• Screening using trepenomal tests may help identify individuals previously treated for syphilis, those with untreated or incompletely treated syphilis, and persons with false-positive results

References

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