(P-BC-67) Real-world Sensitivity and Specificity of Two HIV Serological Screening Test Systems in Blood Donors at a Tertiary Care Hospital, Bangkok, Thailand

Background/Case Studies: We implement two automated immunoassay systems to use alternately for screening HIV infection in our blood donors before further testing with individual HIV, hepatitis B virus and hepatitis C virus nucleic acid testing. We aimed to study the real-world specificity of the two HIV serological screening test systems.

Study

Design/Methods: Our study was approved by the Institute Review (COA no. 993/2024). We reviewed the laboratory record of HIV screening by the two HIV antigen/antibody automated test systems (Alinity i HIV Ag/Ab Combo assay (A system) and Elecsys HIV Duo (E system) from November 2022 to October 2024. All repeatedly reactive (RR) samples by one test system were repeated by another test system, confirmed by immunochromatographic assay (Geenius HIV1/2 Supplemental Assay) and HIV1/2 nucleic acid testing (HIV-NAT) (cobas TaqScreen MPX Test on cobas 6800 platform). We separately analyzed each test system for total number of samples tested, number of repeatedly reactive, results of the cross-check, result of the confirmatory tests calculated and reported sensitivity, specificity, positive predictive value, negative predictive value the indeterminate result from our analysis. All statistical analyses were performed on SPSS and MedCalc software.

Results/Findings: 50,105 donor samples were screened with A system and 53,962 donor samples were screened with E system. There were 34 repeatedly reactive results with A system, 8 samples were confirmed positive (7 samples had positive both immunochromatographic assay and HIV-NAT test and one sample had positive only HIV-NAT and 27 samples had negative confirmation results. The sensitivity was 100% (95% confidence interval [95%CI]: 63.06%-100%), specificity 99.95% (95%CI: 99.92%-99.97%), positive predictive value23.53% (95%CI: 17.32%-31.12%) and negative predictive value 100% (95%CI: 99.99%-100%).There were 40 repeatedly reactive results with E system and 17 were confirmed positive (16 samples had positive immunochromatographic assay and HIV-NAT, one sample had positive only immunochromatographic assay) and 24 samples had negative confirmation test. The sensitivity was 100% (95%CI: 80.94%-100%), specificity 99.96% (95%CI: 99.93%-99.97%), positive predictive 41.46% (95%CI: 32.19%-51.38%) and negative predictive value 100% (95%CI: 99.99%-100%). For crosscheck results, all confirmed positive sample had concordance positive result by both test systems. We exclude one repeatedly reactive result from our analysis due to indeterminate HIV 2 immunochromatography result and negative HIV NAT.

Conclusions: The real-world sensitivity and specificity of the two HIV serological screening systems are high as expected, the negative predictive value is closed to 100%. The confirmation of HIV infection needs both immunochromatography assay and HIV NAT.