【Objective】 To analyze the difference of Ct value of HBsAg-/HBV DNA + in blood samples from different types of voluntary blood donors by double ELISA and HBV DNA (MP6) detection, and to investigate the correlation between Ct value and the frequency of repeated blood donation, the first nucleic acid reactivity and the interval time of previous blood donation, so as to provide reference for laboratory evaluation of the effectiveness of nucleic acid testing(NAT) strategy for repeated blood donors occult hepatitis B virus infection(OBI). 【Methods】 The Ct value and information of blood donors from February 2019 to January 2022 in our laboratory were collected. According to the cumulative number of blood donations, they were divided into two groups:first-time blood donor group (Group A) and repeated blood donor group (Group B). Group B was subdivided into Group C 1( twice of blood donation) and group C 2(three or more times of blood donation) according to the cumulative times of blood donation, and Group D 1(< 1 year), Group D 2(1-3 years), Group D 3(3 years or more) according to the first NAT reactivity and the time of previous blood donation, the difference of Ct value and resolution yeild of HBV DNA in each group was compared. The yeild of HBV DNA in two groups was compared by chi-square test, and the difference of Ct values were compared by Nonparametric test. 【Results】 From February 2019 to January 2022, a total of 270 283 blood donors were tested, including 135 695 in Group A and 134 588 in Group B. The yeild of HBV DNA in Group A was 0.150% (203/135 695), which was higher than that in Group B [0.083% (111/134 588)] (P <0.05).All Ct values were non-normal distribution by normal distribution test, and were expressed as median (quartile), the median values of MP6 and resolution Ct were 37.0(35.9,38.2) and 35.5(33.7,36.9) in Group A, 37.2(36.4,38.1) and 36.5(35.5,37.6) in Group B, respectively. Ct values of MP detection and resolution in Group A, of MP detection and resolution in group B, and of resolution in group A and B were all significant (P<0.05) From the cumulative number of blood donations to compare, the median values of MP detection and resolution Ct were 37.5(36.6,38.3) and 36.5(35.4,37.6) in Group C1,37.1(36.4, 37.9) and 36.6(35.6,37.8) in Group C2, respectively. Significant difference in resolution Ct value between Group A and Group C1, Group A and C2 was noticed(P<0.05), the median values of MP detection Ct in D1, D2 and D3 groups were 37.2(36.3,38), 37.1(36.5,37.9), 37.8(36.6.38.9),respectively, with median resolution CT values at 37.0(35.7,37.8), 35.9(34.8,36.9), 36.9(36.1,37.7), respectively. There was a significant difference in the resolution Ct values between between Group A and D1 and D3 groups (P<0.05), and there was a significant difference between the MP detection and resolution Ct values in D2 Group (P<0.05). The resolution Ct values in D2 and D3 Group were lower than those in D1 Group (P<0.05).The interquartile distribution of Ct values in Group A was wider than that in other groups, and the interquartile distribution of Ct values in Group B was more concentrated. Conclusion The Ct value of HBV DNA detected by nucleic acid in blood donors was correlated with different times of blood donation and different intervals of blood donation. The laboratories of blood station should pay attention to the nucleic acid test results of different types of blood donors to ensure blood safety.

【Objective】 To evaluate the infection status and potential infectivity of Treponema pallidum specific antibody (anti-TP) reactive blood donors, and to provide reference for the key prevention and screening of TP under the current screening strategy. 【Methods】 From February to October 2021, 133 blood donors were tested reactive by two different anti-TP ELISA kits (77 cases were dual-reagent reactive and 56 cases were single-reagent reactive). Syphilis specific IgM antibody (TP-IgM) and IgG antibody (TP-IgG) were detected by Western blot (WB), and TRUST was conducted. The results were analyzed. 【Results】 Of the 133 samples, 24 (18.05%) were positive for TP-IgM, 40 (30.07%) were positive for TP-IgG, and 3 (2.26%) were positive for TRUST. Among them, 12 cases (15.58%) were TP-IgM positive and 40 cases (51.95%) were TP-IgG positive in 77 cases of double reagent reactivity, and 12 cases (21.43%) were TP-IgM positive and 0 was TP-IgG positive in 56 cases of single reagent reactivity. There was no significant difference in the positive rate of TP-IgM between the two groups (P>0.05), while the positive rate of TP-IgG in donors with double reagent reaction was higher than that in donors with single reagent reaction (P<0.05). In addition, among the 133 anti-TP-reactive blood donors, 15 cases were positive for single TP-IgM (11.28%, accounting for 62.50% of the total positive number of TP-IgM, a total of 12 cases of TP-IgM positive among the single reagent reactive patients, and all of them were TP-IgM positive and TP-IgG negative); 30 cases were positive for single TP-IgG (22.56%, accounting for 75.00% of the total positive number of TP-IgG). There were 55 cases (41.35%) who were negative for TP-IgM and TP-IgG, and 8 cases (6.02%) were both positive. 【Conclusion】 The TP-IgM positive donors in anti-TP reactive blood donors are infectious, but the positive rate is not high. Those with single reagent reactivity and single TP-IgM positive are prone to miss detection, which should be controlled. Those who were both TP-IgM and TP-IgG negative and those who were only TP-IgG positive may be false reactivity and the phenomenon of lifelong antibody expression. It is suggested to consider adding TP-IgM detection as a measurement index for permanent deferral of both reagents.

【Objective】 To evaluate the feasibility of confirming syphilis reactive blood donors. 【Methods】 The serum of donors with anti-TP reaction by ELISA were confirmed by treponema pallidum particle agglutination (TPPA) and Western blotting (WB). The results of two confirmation methods that were negative, suspicious or inconsistent were followed up and compared. At the same time, the analytical index values of the screening reagent A, B and C and their combinations were evaluated and compared using the the receiver operating characteristic curve (ROC curve) based on the results of the two confirmation methods. 【Results】 The positive rate of 223 ELISA anti-TP reactive samples (including 124 double-reagent ELISA reactive samples and 99 single-reagent ELISA reactive samples) was 57.40% confirmed by TPPA and 38.57% confirmed by WB (89.52% vs 17.17% by TPPA and 52.42% vs 21.21% by WB for double-reagent and single-reagent ELISA reactive samples). The confirmed negative rate of TPPA was 35.43% and that of WB was 42.60% (6.45% vs 71.72% of TPPA and 29.84% vs 58.59% of WB for double-reagent and single-reagent ELISA reactive samples). According to Kappa test, the confirmed results between the two methods were not consistent, especially for those single-regent ELISA reactive samples. Thirty six cases were followed up successfully, of which 17 (47.22%) confirmed changes in the test results but the changes were irregular. Based on the confirmed results of TPPA and WB, the ROC curve analysis was performed on the anti-TP screening S/CO values of double-reagent ELISA reactive samples. When combining ELISA screening reagents as A/B and A/C, the optimal S/CO values of reagent A were 1.815, 5.73 and 10.205, 16.165, respectively. 【Conclusion】 TPPA and WB have poor consistency in the confirmation of ELISA anti-TP reactive blood samples, and the outcome of follow-up confirmation is unclear. The S/CO threshold of ROC curve is affected by the combination of confirmatory screening reagents, and it is difficult to confirm the results of ELISA anti-TP reactive blood donors.