Compared with the third-generation antibody reagents, the fourth-generation reagents can detect the presence of infection 4–7 days in advance, shortening the “window period”, and is widely used in screening tests5,6. However, the highly sensitive fourth-generation reagents increased the possibility of false positives7. In addition, there are some non-specific factors including hemolysis, lipemia, hyperbilirubinemia and pH value, and specific factors including inflammation, infection, tumor, autoantibodies, heterophile antibodies can also lead to false-positive results8,9,10,11,12.
In this study, Roche Elecsys® HIV combi PT assay was used for screening in women’s and children’s specialized hospital. The specificity and sensitivity of the detection were 99.89% and 100%, and the false positive was 0.11%. The COI value of false-positive samples were significantly lower than that of true positive samples, and almost all false-positive samples were less than 10. With the increase of COI value, the proportion of false-positive samples gradually decreased, and the PPV value increased accordingly, which was consistent in the initial screening test and retest. The detection performance of this study is similar to that of other relevant studies of this reagent4,13,14,15.
Currently, Algorithm adjustments have been shown to reduce the likelihood of false positives in the population8. In this study, fourth-generation reagents were used to reduce the false positive rate of HIV screening. Compared to Roche Elecsys® HIV combi PT assay, Elecsys® HIV DUO assay is an upgraded product on the same test platform, which can reduce false positive results caused by the co-encapsulation of antigens and antibodies. The Abbott Determine HIV Early Detect assay is another mainstream HIV test assay with similar performance to the Roche tests. The samples that were reactive after the initial screening were retested using Roche Elecsys® HIV DUO assay and Abbott Determine HIV Early Detect assay, with false-positive rate reduced to 0.04% and the specificity of the algorithm increased to 99.96%. This shows that the detection performance is indeed optimized.
As the study group is mainly women and children, the clinical diagnosis of false positive samples focuses on pregnancy, benign or malignant gynecological tumors and infertility, and female patients account for a relatively large proportion, most of which are adult women over 15 years old. Adult women experience more pathophysiological changes, such as pregnancy and autoimmune diseases. These processes may cause complex immune responses, which can affect the detection of serological indicators. For pregnant women, prenatal HIV screening facilitates early diagnosis and treatment, as well as preventing mother-to-child transmission of HIV during pregnancy, delivery and breastfeeding16. However, for low false-positive results, antibody confirmatory tests often do not confirm the status of infection, while sensitive RNA tests can help rule out viral infection. Therefore, a more specific HIV-1/2 test should be added to the HIV test to improve the accuracy and reliability of the HIV test results17. At the screening stage, the adoption of appropriate testing algorithm helps to improve the efficiency of HIV screening, but also reduces the waste of clinical resources18,19.
There are still some limitations to this study. First of all, the study data came from women and children’s specialized hospital, and the testing algorithm adopted in the study needs to be verified by data from multi-regions and multi-centers. Secondly, as a retrospective study, some predictions can be made based on the existing research results to play a certain prospective role.
In general, with the wider development and application of fourth-generation reagents, retesting with reagents such as Roche Elecsys® HIV DUO assay, which can detect antigens and antibodies separately, can indeed improve the performance of testing algorithm, while reducing diagnostic time and laboratory costs, and ultimately improve healthcare.
