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| Establishment of the Gray Zone Range for Treponema Pallidum Antibody (TP-Ab) Detection by Chemiluminescent Microparticle Immunoassay Based on Regression Equation |
| LIANG Dong-xiang, SU Xiao-jing, HUANG Qiao-li |
| Longyan First Affiliated Hospital of Fujian Medical University,Longyan Fujian 364000, China |
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Abstract Objective: To apply a regression equation to calculate the gray zone range for detecting Treponema pallidum antibody (TP-Ab) in blood samples using the ARCHITECT i2000SR fully automated microparticle chemiluminescence analyzer. Methods: A total of 180 blood samples initially screened for syphilis antibodies in our hospital were collected, which were tested using both the Treponema pallidum chemiluminescent microparticle immunoassay (TP-CMIA) on the ARCHITECT i2000SR electrochemical luminescence analyzer and the Treponema pallidum particle agglutination assay (TPPA). The optimal regression equation was established based on the TPPA cut-off index (COI) values and positive predictive probability, which was then used to determine the gray zone range for TP-CMIA. Results: This study analyzed 180 serum samples using a binary logistic regression model to evaluate the predictive value of COI values determined by the TP-CMIA method for syphilis. The Hosmer-Lemeshow test yielded P=0.332, further confirming the model's goodness-of-fit. The COI value was identified as a sensitive predictor of syphilis, with the cubic curve model demonstrating optimal fitting performance (R2=0.925). When the positive predictive probability reached 95%, the corresponding COI value was 5.353, indicating that samples with COI values exceeding 5.353 had a true-positive probability >95%. Consequently, the gray zone range for TP-CMIA COI values was defined as 1.000-5.353, with values below this range classified as a false-positive interval. The model accurately classified 98.7% of syphilis cases and 87.0% of non-syphilis cases, achieving an overall correct classification rate of 97.2%. Conclusion: The gray zone range for COI values of TP-Ab detected by the TP-CMIA method (ARCHITECT i2000SR) was established as 1.000-5.353 using a regression equation, with samples showing COI values≤5.353 carrying a potential false-positive risk.
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Received: 10 June 2024
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Corresponding Authors:
HUANG Qiao-li, E-mail: 392308405@qq.com
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