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]

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Overview

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

Laboratory Findings

• 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 eachother

Trepenomal tests

• Include
• Antibody titres once positive remains positive for the rest of 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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