Re-entry mechanism of blood donors with single-reagent reactive syphilis ELISA results based on S/CO values and TPPA confirmatory results
10.13303/j.cjbt.issn.1004-549x.2026.08.018
- VernacularTitle:基于ELISA S/CO值与TPPA确证结果的梅毒单试剂阳性献血者归队机制研究
- Author:
Zhanghui LI
1
;
Wenjia HU
1
;
Tao FENG
1
;
Chen WU
1
;
Nizhen JIANG
1
Author Information
1. Jiangsu Province Blood Center, Nanjing 210042, China
- Publication Type:Journal Article
- Keywords:
treponema pallidum;
enzyme-linked immunosorbent assay;
S/CO value;
TPPA;
blood donor re-entry;
ROC curve
- From:
Chinese Journal of Blood Transfusion
2026;39(8):1117-1124
- CountryChina
- Language:Chinese
-
Abstract:
Objective: To evaluate the feasibility of re-entry for blood donors deferred for single-reagent reactive anti-TP ELISA results, to assess the ability of ELISA S/CO values of different kits to discriminate true-from false-positive samples and to determine the optimal cutoff value for each kit, thereby providing a scientific basis for improving blood donor reentry strategies. Methods: Data of two donor cohorts were retrospectively collected: (1) a re-entry cohort of 106 donors who applied for re-entry at Jiangsu Province Blood Center from January 1, 2018 to December 31, 2025, all previously deferred for single-reagent reactive anti-TP ELISA results (58 reactive with the Xinchuang kit and 48 with the Kehua kit); (2) a routine screening confirmation cohort of 39 donors found to be single-reagent reactive in routine donation screening and additionally tested by TPPA between April 2024 and June 2026 (17 Xinchuang and 22 Kehua). Using TPPA results as the gold standard, the two cohorts were pooled (75 Xinchuang, 70 Kehua), and receiver operating characteristic (ROC) curves were constructed separately for each kit. The 95% confidence interval (CI) of the area under the curve (AUC) was estimated with 2 000 bootstrap replicates, and the optimal S/CO cutoff of each kit was determined by the maximum Youden index; sensitivity analysis was performed by cohort source. In addition, TPPA-confirmed positivity rates were compared between single-and dual-reagent reactive samples at re-entry testing. Results: Of the 106 donors in the re-entry cohort, 73 were successfully requalified and 33 failed. The mean S/CO value at deferral testing in successfully requalified donors was 1.930 (median 1.570), significantly lower than 3.487 (median 2.592) in failed donors (P<0.001). Among the 33 donors who failed requalification, 16 samples were TPPA positive; at re-entry testing, 7 were dual-reagent reactive (6 TPPA positive), 25 remained single-reagent reactive (9 TPPA positive), and 1 was ELISA non-reactive (TPPA positive). The TPPA positivity rate of dual-reagent reactive samples at re-entry testing was 85.7% (6/7), significantly higher than 36.0% (9/25) of single-reagent reactive samples (P=0.033); the agreement between the two kits at re-entry testing was poor (Kappa=0.231). ROC analysis of pooled samples showed that for the Xinchuang kit (n=75, 14 TPPA positive), the AUC was 0.837 (95%CI:0.731-0.929) with an optimal cutoff of 2.025, corresponding to a sensitivity of 92.9% (13/14), a specificity of 65.6% (40/61) and a negative predictive value of 97.6% (40/41); for the Kehua kit (n=70, 13 TPPA positive), the AUC was 0.787 (95%CI:0.649-0.900) with an optimal cutoff of 1.733, corresponding to a sensitivity of 92.3% (12/13), a specificity of 56.1% (32/57) and a negative predictive value of 97.0% (32/33). Sensitivity analysis by cohort showed that the AUCs calculated separately for the re-entry and screening cohorts were consistent in direction with the pooled analysis. Conclusion: S/CO values of both the Xinchuang and Kehua ELISA kits can discriminate TPPA-confirmed true from false positives, but their optimal cutoffs differ. Dual-reagent reactivity at re-entry testing strongly indicates TPPA-confirmed positivity; the TPPA positivity rate of single-reagent reactive samples increases in a gradient with rising S/CO values, and single-reagent reactive samples with low S/CO values are mostly false positives. Incorporating kit-specific stratified management based on quantitative S/CO thresholds into the re-entry mechanism may help establish a fast-track re-entry pathway for low-risk false-positive donors.
