The Evaluation Of Low Cut-Off Index Values Of Elecsys (R) Hiv Combi Pt Assay In Predicting False-Positive Results

Objective: To analyze the results of different cut-off index (COI) values of Elecsys (R) HIV combi PT assay and to assess the role of COI in reducing the frequency of false-positive results.Methods: We conducted a retrospective study of samples analyzed by Elecsys (R) HIV combi PT assay, a 4th-generation ECLIA, between 2016 and 2017. A total amount of 379 122 samples were collected for HIV (Human Immunodeficiency Virus) screening.Results: A total of 379 122 samples were analyzed. 2528 (0.67%) were positive by Elecsys (R) HIV combi PT. Of these, 468 were false-positive results, and most of them (94.87%) were in samples with 1 < COI < 15. The false-positive rate was 0.12%. Patients with false-positive samples were more distributed in elder (P <.001) and female (P <.001) than true-positive specimens. The median COI in true-positive specimens was (385.20), which is significantly higher than false-positive specimens (2.08). The consistency between Elecsys (R) HIV combi PT assay and 3rd-generation and positive predictive value (PPV) increased with higher COI values. Cancer, infection, and neurological diseases were considered the potential confounding factors of HIV false-positive results (19.44%, 11.11%, and 6.62%, respectively).Conclusion: Samples with low COI values, especially those contain confounding factors, need to be further scrutinized to determine whether the confounding factors may cause false-positive problem. In addition, the hypothesis that low COI values may predict false-positive results is valid.