Evaluation of the Signal-to-Cutoff Ratio of the Roche Elecsys HIV Ag/Ab Test for Predicting HIV-1 Infection in a Tertiary Care Hospital in Ankara, Türkiye

Öz

Background: False-positive results are common in HIV screening, particularly in low-prevalence settings where enzyme immunoassay-based methods are used. Accurate discrimination between true and false reactivity is essential for timely diagnosis, reducing patient anxiety, and preventing unnecessary follow-up procedures. To evaluate the diagnostic performance of the signal-to-cutoff (S/CO) ratio in predicting true HIV-1 infection in a tertiary care hospital setting using a fourth-generation HIV Ag/Ab assay. Methods: In this retrospective study, 715 reactive serum samples collected between January 2022 and December 2024 were analyzed. HIV screening was performed using a fourth-generation chemiluminescent microparticle immunoassay. Repeatedly reactive samples were subjected to confirmatory testing based on immunochromatographic principles. The optimal S/CO threshold for predicting true HIV infection was determined using receiver operating characteristic (ROC) analysis. Results: Out of 715 reactive samples, 309 (43.2%) were confirmed as true positives, while 406 (56.8%) were false positives. All false positives had S/CO values <100, and no true positives were identified among samples with S/CO <2.30. The median S/CO value for true positives was 738.0 (IQR: 239–1337), compared to 1.72 (IQR: 1.20–3.33) in false positives (p<0.001). ROC analysis identified an optimal S/CO threshold of 29.7, which yielded an area under curve of 0.997, with 97.1% sensitivity, 99.1% specificity, 91.6% positive predictive value, and 99.7% negative predictive value. The false-positive rate decreased from 56.8% at the ≥1.0 threshold to 1.96% at the ≥29.7 threshold. Conclusion: The S/CO ratio in fourth-generation HIV Ag/Ab assays demonstrates high predictive accuracy for HIV infection. An S/CO threshold of ≥29.7 effectively reduces false-positive rates while maintaining diagnostic sensitivity, providing a valuable tool for clinical decision-making prior to confirmatory testing.

Anahtar Kelimeler

• HIV
• chemiluminescent microparticle immunoassay
• sensitivity
• specificity
• ROC analysis

Kaynakça

1. 1. Coffin J, Blomberg J, Fan H, Gifford R, Hatziioannou T, Lindemann et al. ICTV Report Consortium. ICTV Virus Taxonomy Profile: Retroviridae 2021. J Gen Virol. 2021;102:001712. https://doi.org/10.1099/jgv.0.001712
2. 2. World Health Organization (WHO). (2024). HIV data and statistics. https://www.who.int/teams/global-hiv-hepatitis-and-stis-programmes/hiv/strategic-information/hiv-data-and-statistics
3. 3. Duncan D, Duncan J, Kramer B, Nilsson AY, Haile B, Butcher A. et al. An HIV Diagnostic Testing Algorithm Using the cobas HIV-1/HIV-2 Qualitative Assay for HIV Type Differentiation and Confirmation. J Clin Microbiol. 2021;59:e0303020. https://doi.org/10.1128/JCM.03030-20
4. 4. Republic of Türkiye Ministry of Health, General Directorate of Public Health. 2023 Unit Activity Report. Ankara: Ministry of Health; 2024.
5. 5. Gökengin D. HIV infection in Turkey: How close are we to the target? Klimik Derg. 2018;31:4–10. https://doi.org/10.5152/kd.2018.04
6. 6. Albritton WL, Vittinghoff E, Padian NS. Human immunodeficiency virus testing for patient-based and population-based diagnosis. J Infect Dis. 1996;174 (Suppl 2):S176-S181. https://doi.org/10.1093/infdis/174.Supplement_2.S176
7. 7. CDC Guidelines for Laboratory Testing for the Diagnosis of HIV Infection: Updated Recommendations. Available from: https://www.cdc.gov/hiv/pdf /guidelines_testing_ labtestingdcl.pdf
8. 8. Luo W, Sullivan V, Smith T, Peters PJ, Gay C, Westheimer E, et al. Performance evaluation of the Bio-Rad Geenius HIV 1/2 supplemental assay. J Clin Virol. 2019;111:24–28. https://doi.org/10.1016/j.jcv.2018.12.006

9. 9. Branson BM. HIV Diagnostics: Current Recommendations and Opportunities for Improvement. Infect Dis Clin North Am. 2019;33:611–628. https://doi.org/10.1016/j.idc.2019.04.001
10. 10. Augusto ÂDR, Iriemenam NC, Kohatsu L, de Sousa L, Maueia C, Hara C, et al. High level of HIV false positives using EIA-based algorithm in survey: Importance of confirmatory testing. PLoS One. 2020;15:e0239782. https://doi.org/10.1371/journal.pone.0239782
11. 11. Orak F, Doğaner A, Yalçınkaya KT, Aral M. An evaluation of the effect of the clinical features of patients and the drugs used on the false-positive EIA test for HIV. Erciyes Med J. 2021;43:465–469. https://doi.org/10.14744/etd.2021.34682
12. 12. Everett DB, Baisely KJ, McNerney R, Hambleton I, Chirwa T, Ross DA, et al. Association of schistosomiasis with false-positive HIV test results in an African adolescent population. J Clin Microbiol. 2010;48:1570–1577. https://doi.org/10.1128/JCM.02264-09
13. 13. Kim S, Lee JH, Choi JY, Kim JM, Kim HS. False-positive rate of a “fourth-generation” HIV antigen/antibody combination assay in an area of low HIV prevalence. Clin Vaccine Immunol. 2010;17:1642–1644. https://doi.org/10.1128/CVI.00258-10
14. 14. Bhattacharya R, Barton S, Catalan J. When good news is bad news: psychological impact of false positive diagnosis of HIV. AIDS Care. 2008;20(5):560–564. https://doi.org/10.1080/09540120701867206
15. 15. Technical update on HIV-1/2 differentiation assays. Available from: https://stacks.cdc.gov/view/cdc/40790
16. 16. Shida S, Takahashi N, Fujishima N, Kameoka Y, Nara M, Fujishima M, et al. False-positive human immunodeficiency virus antibody test and autoimmune hemolytic anemia in a patient with angioimmunoblastic T-cell lymphoma. Intern Med. 2011;50:2383–2387. https://doi.org/10.2169/internalmedicine.50.5764
17. 17. Wang L, Wang JY, Tian XD, Ruan JX, Yu Y, Yan F. Sample-to-cutoff ratios using Architect HIV Ag/Ab Combo: the influence with the results of supplemental tests and optimal cutoff value to predict HIV infection. J Clin Lab Anal. 2019;33:e22866. https://doi.org/10.1002/jcla.22866
18. 18. Kosack CS, Page AL, Beelaert G, Benson T, Savane A, Ng’ang’a A, et al. Towards more accurate HIV testing in sub-Saharan Africa: a multi-site evaluation of HIV RDTs and risk factors for false positives. J Int AIDS Soc. 2017;19:21345. https://doi.org/10.7448/IAS.20.1.21345
19. 19. Klarkowski D, O’Brien DP, Shanks L, Singh KP. Causes of false-positive HIV rapid diagnostic test results. Expert Rev Anti Infect Ther. 2014;12:49–62. https://doi.org/10.1586/14787210.2014.866516
20. 20. Sheikh AA, Sheikh AS, Sheikh NS, Shan RU, Malik MT, Afridi F. High frequency of false positive results in HIV screening in blood banks. J Pak Med Assoc. 2006;56(1 Suppl 1):S72-S75.
21. 21. Malm K, von Sydow M, Andersson S. Performance of three automated fourth-generation combined HIV antigen/antibody assays in large-scale screening of blood donors and clinical samples. Transfus Med. 2009;19:78–88. https://doi.org/10.1111/j.1365-3148.2009.00907.x
22. 22. Yılmaz E, Karabulut N, İstanbullu-Tosun A, Alaçam S, Şahin M, Alp E, et al. Reactive fourth-generation HIV assays at low cut-off indices may be clinically misleading in the obstetric setting: a multicenter analysis of 904 reactive cases. Int J Infect Dis. 2026;170:108929. https://doi.org/10.1016/j.ijid.2026.108929
23. 23. Shima-Sano T, Yamada R, Sekita K, Hankins RW, Hori H, Seto et al. A human immunodeficiency virus screening algorithm to address the high rate of false-positive results in pregnant women in Japan. PLoS One. 2010;5:e9382. https://doi.org/10.1371/journal.pone.0009382
24. 24. Zhu W, Bessler P, Lale A, Delaney K, O’Shea J, Huang YA, et al. Real-world positive predictive value and false-positive rates of laboratory-based HIV antigen/antibody testing by age and sex—United States, 2019–2024. J Acquir Immune Defic Syndr. 2026;101:513–519. https://doi.org/10.1097/QAI.0000000000003823
25. 25. Chacón L, Mateos ML, Holguín Á. Relevance of cutoff on a 4th generation ELISA performance in the false positive rate during HIV diagnostic in a low HIV prevalence setting. J Clin Virol. 2017;92:11–13. https://doi.org/10.1016/j.jcv.2017.04.014
26. 26. Cui C, Ping L, Feng Z, Xin R, Yan C, Li Z. Evaluation of the clinical effectiveness of HIV antigen/antibody screening using a chemiluminescence microparticle immunoassay. J Virol Methods. 2015;214:33–36. https://doi.org/10.1016/j.jviromet.2014.07.026
27. 27. Alonso R, Pérez-García F, Gijón P, Collazos A, Bouza E. Evaluation of the Architect HIV Ag/Ab Combo Assay in a low-prevalence setting: the role of samples with a low S/CO ratio. J Clin Virol. 2018;103:43–47. https://doi.org/10.1016/j.jcv.2018.04.002
28. 28. Jensen TO, Robertson P, Whybin R, Chambers I, Lahra M, Rawlinson W, et al. signal-to-cutoff ratio in the Abbott architect HIV Ag/Ab Combo assay that predicts subsequent confirmation of HIV-1 infection in a low-prevalence setting. J Clin Microbiol. 2015;53:1709–1711. https://doi.org/10.1128/JCM.03583-14
29. 29. Zacharias NM, Athanassaki ID, Sangi-Haghpeykar H, Gardner MO. High false-positive rate of human immunodeficiency virus rapid serum screening in a predominantly hispanic prenatal population. J Perinatol. 2004;24:743–747. https://doi.org/10.1038/sj.jp.7211184
30. 30. Liu P, Jackson P, Shaw N, Heysell S. Spectrum of false positivity for the fourth generation human immunodeficiency virus diagnostic tests. AIDS Res Ther. 2016;13:1–5. https://doi.org/10.1186/s12981-015-0086-3
31. 31. Alexander TS. Human Immunodeficiency Virus Diagnostic Testing: 30 Years of Evolution. Clin Vaccine Immunol. 2016 Apr 4;23(4):249-53. https://doi.org/10.1128/CVI.00053-16
32. 32. Zucker J, Carnevale C, Gordon P, Sobieszczyk ME, Rai AJ. Am I positive? Improving Human immunodeficiency virus testing in the era of preexposure prophylaxis and immediate antiretroviral therapy using machine learning. Open Forum Infect Dis. 2022;9:ofac259. https://doi.org/10.1093/ofid/ofac259
33. 33. Xia X, Zhang X, Zhou J, Zhang M. An analysis of predictive sample-to-cutoff index for HIV infection confirmation using Elecsys® HIV Combi PT assay. Int J Clin Pract. 2022;2022:5097189. https://doi.org/10.1155/2022/5097189
34. 34. White DAE, Anderson ES, Basham K, Ng VL, Russell C, Lyons MS, et al. Clinical utility of the signal-to-cutoff ratio of reactive HIV antigen/antibody screening tests in guiding emergency physician management. J Acquir Immune Defic Syndr. 2022;89:332–339. https://doi.org/10.1097/QAI.0000000000002873
35. 35. Yaman M, Bakır A, Karabulut N, Alaçam S, Köksal MO, Ağaçfidan A. Evaluation of signal cut-off ratio with fourth generation HIV Ag/Ab screening test for the diagnosis of HIV infection. Smyrna Tıp Derg. 2023;2(1):1–7.
36. 36. Chao TT, Sheffield JS, Wendel GD Jr, Ansari MQ, McIntire DD, Roberts SW. Risk factors associated with false positive HIV test results in a low-risk urban obstetric population. J Pregnancy. 2012;2012:841979. https://doi.org/10.1155/2012/841979
37. 37. Acar A, Kemahli S, Altunay H, Kosan E, Oncul O, Gorenek L, et al. The significance of repeat testing in Turkish blood donors screened with HBV, HCV and HIV immunoassays and the importance of S/CO ratios in the interpretation of HCV/HIV screening test results and as a determinant for further confirmatory testing. Transfus Med. 2010;20:152–159. https://doi.org/10.1111/j.1365-3148.2009.00987.x