2.1 Basic information of serum samples
From August 2018 to December 2019, 3972 of the 106,757 samples were detected with anti-TP antibodies by ELISA were initially positive (S/CO≥1) or negative (S/CO < 1 but showed chromogeny on the ELISA plate). The TPPA retest showed that 3809 samples were positive. The results of ELISA and TPPA were inconsistent in 163 serum samples, accounting for 4.1% (163/3 972) of the total retest samples. Of 163 samples, 29 were ELISA-/TPPA+ or ELISA-/TPPAreserved, accounting for 17.8% (29/163); and 134 were ELISA+ /TPPA- or ELISA+/TPPAreserved, accounting for 82.2% (134/163). The patients included 101 men (61.96%) and 62 women (38.04%). The age of patients ranged from 4 days to 89 years (53.6 ± 17.5). As shown in Table 1, anti-TP antibodies were detected by ELISA and TPPA, and the difference in results was statistically significant (P < 0.05).
2.2 Retest and confirmation results of negative samples by ELISA
As shown in Table 2,among 163 samples with suspicious results of anti-TP antibodies, 29 samples were negative by ELISA (17.8%). Among them, the TPPA retest was positive in 22 cases and reserved in 7 cases; while WB was positive in 13 cases, suspicious in 9 cases, and negative in 7 cases. The S/CO values of the 29 samples ranged from 0.201 to 0.984. The S/CO was <0.5 in seven samples. The TPPA retest was positive in six cases and reserved in one case, while WB was positive in three cases, suspicious in three cases, and negative in one case. Further, in 22 samples, 0.5 ≤ S/CO <1. The TPPA retest was positive in 16 cases and reserved in 6 cases, while WB was positive in 10 cases, suspicious in 6 cases, and negative in 6 cases.
2.3 Retest and confirmation results of positive samples by ELISA
As shown in Table 3,among 163 samples with suspicious results of anti-TP antibodies, 134 samples were positive by ELISA (17.8%). Among them, the TPPA retest was negative in 76 cases and reserved in 58 cases, while WB was positive in 18 cases, suspicious in 30 cases, and negative in 86 cases. The S/CO values of the 134 samples ranged from 1.01 to 19.15. In 54 samples, 1 ≤S/CO <2. The TPPA retest was negative in 42 cases and reserved in 12 cases, while WB was positive in 7 cases, suspicious in 7 cases, and negative in 40 cases. In 32 samples, 2 ≤S/CO <3. The TPPA retest was negative in 17 cases and reserved in 15 cases, WB was positive in 1 case, suspicious in 11 cases, and negative in 20 cases. In 27 samples, 3 ≤ S/CO < 5. The TPPA retest was negative in 12 cases and reserved in 15 cases, while WB was positive in 4 cases, suspicious in 8 cases, and negative in 15 cases. In 21 samples, S/CO ≥5. The TPPA retest was negative in 5 cases and reserved in 16 cases, while WB was positive in 6 cases, suspicious in 4 cases, and negative in 11 cases.
2.4 Comparison of the test results of ELISA and WB in 163 samples
The results of WB-IgM and WB-IgG in 163 samples with different results of ELISA and TPPA were analyzed. As shown in Table 4, among the 29 ELISA-negative samples, WB results were negative in 7 cases, positive in 13 cases, and suspicious in 9 cases. Among 134 ELISA-positive samples, 86 cases were negative, 18 cases were positive, and 30 cases were suspicious, with a specificity of 7.53% (7/93) and a sensitivity of 58.06% (18/31). Significant differences were found between ELISA and WB in detecting anti-TP antibodies (P< 0.05).
2.5 Comparison of the test results of TPPA and WB in 163 samples
The results of WB-IgM and WB-IgG in 163 samples with different results of ELISA and TPPA were analyzed. As shown in Table 5,among the 76 TPPA-negative samples, WB results were negative in 59 cases, positive in 9 cases, and suspicious in 8 cases. Among the 22 TPPA-positive samples, WB results were negative in 2 cases, positive in 13 cases, and suspicious in 7 cases, with a specificity of 63.44% (59/93) and a sensitivity of 41.94% (13/31). Significant differences were found between TPPA and WB in detecting anti-TP antibodies (P< 0.05).