WHO/PAHO Collaborating Centre for Syphilis Serology Proficiency Testing Program at the CDC

Background: Proficiency in serological testing is essential to accurately diagnose syphilis. CDC administers a syphilis serology proficiency testing (PT) program worldwide in its role as a WHO/PAHO Collaborating Centre for STD Diagnostics and Surveillance.

Methods:CDC sends a serum panel of known results to 78 laboratories worldwide. Participating laboratories perform treponemal (TPPA, MHA-TP, TPHA, FTA-ABS, EIA) and non-treponemal (VDRL, USR, RPR) qualitative and quantitative tests, reporting results to CDC for analysis and feedback.

Results: In 2012, 51(65.4%) of the 78 laboratories reported PT results on at least one serologic test (third panel). Qualitative VDRL and RPR non-treponemal test results from responding laboratories were comparable to those of 3 CDC reference laboratories (Georgia PHL; the Texas Department of State Health Services; and the Syphilis Serology Laboratory, CDC) for most VDRL and RPR samples.  For the qualitative VDRL, scores averaged 98.7 %, with 1 of 31(3.2%) reporting laboratories failing. Scores for the qualitative RPR averaged 99.4%, with 1 of 36 (2.7%) laboratories failing. For the quantitative VDRL and RPR, low scores were due to reported titers being too high or too low. Scores for the quantitative VDRL averaged 94.1%, with 3 of 29(10.3%) laboratories failing. Scores for the quantitative RPR averaged 94%, with 6 of 32(18.8 %) laboratories failing. For treponemal tests, the 42 laboratories performing the MHA-TP, TPHA, or TPPA averaged 98.6%; 3 (7.2%) laboratories failed. For FTA-ABS, 22 laboratories averaged 100%. For the EIA-IgG test, 18 laboratories averaged 98.9% with 1 (5.6%) not achieving an acceptable result. 

Conclusions: Laboratories participating in the syphilis PT program do well in treponemal and qualitative non-treponemal testing. However, several had problems in quantitative non-treponemal tests suggesting training or other capacity building options may be beneficial. Criteria for PT program inclusion should be revisited due to lack of reporting from a number of laboratories.