What is the screening test of choice for syphilis (Sexually Transmitted Infection)?

From the Guidelines

The screening test of choice for syphilis is the treponemal test, such as an EIA or chemiluminescence immunoassay, due to its high specificity and ability to identify persons previously positive, treated, and/or partially treated for syphilis. This approach is supported by the 2018 update by the Infectious Diseases Society of America and the American Society for Microbiology, which suggests that many high-volume clinical laboratories have reversed the testing sequence and begin the testing algorithm first with a specific treponemal test 1.

Key Points to Consider

• The traditional approach of using non-treponemal tests, such as RPR, as the initial screening test is still widely used, but it has a high percentage of false-positive results in many medical conditions unrelated to syphilis 1.
• Treponemal tests, such as EIA or chemiluminescence immunoassay, are more specific and can identify persons previously positive, treated, and/or partially treated for syphilis, as well as yield false positives in patients with low likelihood of infection 1.
• If a treponemal test is positive, it should be confirmed with a non-treponemal test, such as RPR, to guide management decisions 1.
• Non-treponemal tests typically become negative after successful treatment, while treponemal tests usually remain positive for life regardless of treatment, making non-treponemal tests more useful for monitoring treatment effectiveness and detecting reinfection.

Testing Algorithm

• The recommended testing algorithm is to start with a treponemal test, such as an EIA or chemiluminescence immunoassay, and then confirm positives with a non-treponemal test, such as RPR 1.
• If the follow-up confirmation test (RPR) is negative, it may require the laboratory to perform a different treponemal-specific test to guide management decisions, such as fluorescent treponemal antibody–absorbed 1.

From the Research

Screening Tests for Syphilis

The screening tests for syphilis include:

• Venereal Disease Research Laboratory (VDRL) test 2
• Rapid Plasma Reagin (RPR) test 2, 3, 4, 5
• Treponema pallidum particle agglutination test (TPPA) 4
• Fluorescent Treponemal Antibody Absorption (FTA-ABS) test 2, 6
• Immunochromatographic test (Biorapid Syphilis) 4
• Enzyme-linked immunosorbent assay (ELISA) 4, 6, 5

Characteristics of Screening Tests

The characteristics of these screening tests are:

• Sensitivity and specificity: The sensitivity and specificity of the Biorapid Syphilis, Bioelisa Syphilis 3.0, and ETI-Treponema Plus were 92% and 79%, 100% and 100%, and 100% and 100%, respectively 4
• Agreement between tests: The agreements of the FTA-ABS with the TPHA test, the TPPA test, the ICE test, and the TP test were 97.5%, 95.9%, 98.3%, and 98.3%, respectively 6
• Comparison with standard tests: The CAPTIA Syphilis-G enzyme immunoassay was compared with the standard RPR test and showed improved sensitivity and specificity 5

Choice of Screening Test

The choice of screening test for syphilis depends on various factors, including:

• Availability of resources: The RPR test and VDRL test are widely used due to their simplicity and low cost 2, 3
• Population being tested: The TPPA test is commonly used outside Europe, while the RPR test or VDRL test is most often used for screening purposes 4
• Need for rapid results: The immunochromatographic test (Biorapid Syphilis) can provide rapid results, but its sensitivity and specificity may be lower than other tests 4