An evaluation of recurrent syphilis positivity in blood bank donors

To ensure safe blood transfusion in blood centers, syphilis infection should be identified precisely and rapidly, using an appropriate test method. The recommended algorithms to be used in blood centers include the reconfirmation of the positivity detected via screening tests, using advanced diagnostic methods. The main goal of the present study is to determine the index S/Co value that eliminates the necessity of reconfirmation tests when ?Architect® Syphilis TP? test, which uses CMIA technology, is applied. The secondary goals of the study are the evaluation of the RPR test results of the samples detected as positive by the ?Architect® Syphilis TP? test, and the analysis of the antibody responses to the treponemal antigens (TpN15, TpN17, TpN47 and TmpA) used in the reference method. In the light of our findings, we have also set forth a diagnosis algorithm that is applicable for syphilis screening to be performed in blood centers using the ?Architect® Syphilis TP? test.In the present study, WB IgG/IgM and RPR tests were conducted for 177 serum samples detected as recurrent positive by the ?Architect® Syphilis TP? test between 20.07.2006 and 10.11.2008. The results were evaluated using ROC analysis and an index S/Co value was set.The index was determined as 7.19 S/Co by the ROC analysis. According to the results of the study, S/Co values of 107 samples (60.5%) were found to be lower than 7.19 (these samples constitute the ?<7.19? group). Only three of these samples (6.4%) were confirmed by WB. The remaining 104 (92.9%) samples were negative by WB, therefore considered false positive. As for the group with an S/Co value equal to or greater than 7.19 (the ??7.19? group), 95.4% of the samples were confirmed as positive using the WB test. In 69.8% of the WB-positive samples, the WB test revealed reactivity in all four antigen regions. Reactivity was most pronounced in the TpN47 and least pronounced in the TmpA regions. The RPR test revealed positivity in 39 (22%) serum samples. Seven (18%) of these RPR positive samples were in the ?<7.19? group, and were all WB negative. 32 (82%) RPR positive samples belonged to the ??7.19? group and 31 of these samples were also WB positive. When all samples are taken into account, RPR test yielded positive results in only 31 (48%) of the samples which were positive in the WB test.In conclusion, a diagnosis algorithm was set forth according to the S/Co index value of ?7.19?, which was set for the ?Architect® Syphilis TP? test. It was concluded that the use of RPR as a donor screening test is particularly inconvenient for the selection of donors in blood centers.Key Words: Syphilis, blood center, Sample/ threshold value, Western Blot, RPR, CMIA