Comparison between treponemal and non-treponemal tests for syphilis detection

Area of Science:

• Medical diagnostics
• Infectious disease research
• Clinical laboratory science

Background:

• Syphilis diagnosis traditionally uses a two-step algorithm: non-treponemal screening followed by treponemal confirmation.
• This algorithm is globally implemented for syphilis detection, including in blood donation settings.

Purpose of the Study:

• To assess the performance of various treponemal and non-treponemal syphilis tests in blood donors.
• To evaluate the effectiveness of different diagnostic assays in identifying syphilis infections.

Main Methods:

• A cross-sectional study involving 384 blood donor samples initially reactive for syphilis using the VDRL test.
• Samples were re-tested with VDRL, ELISA, CLIA, and FTA-ABS (confirmatory).
• Agreement was assessed using kappa coefficients, and performance indices (sensitivity, predictive values) were calculated.

Main Results:

• Concordance rates varied between tests, with ELISA and CLIA showing higher agreement (78.8% and 76% with VDRL, respectively).
• Treponemal tests (FTA-ABS) showed lower concordance (44.2%-61.9%) when compared to non-treponemal and other treponemal assays.
• Sensitivity ranged from 89.70% to 99.39%. CLIA had the highest positive predictive value (95.27%), while VDRL showed the highest false-positive rate (94.52%).

Conclusions:

• The study highlights the agreement between certain non-treponemal and treponemal syphilis tests.
• The CLIA test emerged as a promising assay with a high positive predictive value for syphilis detection in blood donors.
• While initial sample reactivity may influence results, the findings offer insights into current syphilis diagnostic algorithms.