Causes of false-positive HIV rapid diagnostic test results

Abstract

HIV rapid diagnostic tests have enabled widespread implementation of HIV programs in resource-limited settings. If the tests used in the diagnostic algorithm are susceptible to the same cause for false positivity, a false-positive diagnosis may result in devastating consequences. In resource-limited settings, the lack of routine confirmatory testing, compounded by incorrect interpretation of weak positive test lines and use of tie-breaker algorithms, can leave a false-positive diagnosis undetected. We propose that heightened CD5⁺ and early B-lymphocyte response polyclonal cross-reactivity are a major cause of HIV false positivity in certain settings; thus, test performance may vary significantly in different geographical areas and populations. There is an urgent need for policy makers to recognize that HIV rapid diagnostic tests are screening tests and mandate confirmatory testing before reporting an HIV-positive result. In addition, weak positive results should not be recognized as valid except in the screening of blood donors.

Keywords::

• algorithms
• diagnosis
• discordant
• false positive
• HIV
• humanitarian
• Médecins Sans Frontières
• rapid diagnostic test
• resource-limited setting
• resource-poor setting

Author contributions

D Klarkowski was the originator of the article, did the first draft and literature search. KP Singh analyzed and synthesized information and completed the second draft of the manuscript. D O’Brien worked on subsequent drafts. L Shanks worked on subsequent drafts. All authors approved the final version of the article.

Acknowledgements

The authors thank S Venis and C Montgomery for editing assistance.

Financial & competing interests disclosure

The authors have no relevant affiliations or financial involvement with any organization or entity with a financial interest in or financial conflict with the subject matter or materials discussed in the manuscript. This includes employment, consultancies, honoraria, stock ownership or options, expert testimony, grants or patents received or pending or royalties.

No writing assistance was utilized in the production of this manuscript.

Key issues

• HIV rapid diagnostic tests (RDTs) have enabled widespread implementation of HIV programs and surveillance in resource-limited settings, but false-positive results from HIV RDTs can go undetected in these settings because of the lack of routine confirmatory testing.

• Interpretation of weak positive test lines as positives instead of indeterminate increases the risk of falsely diagnosing HIV on RDTs. HIV RDTs use a restricted number of viral target antigens, increasing susceptibility to false-positive results.

• The tie-breaker algorithm is highly susceptible to error when false positives are caused by cross-reactive antibodies and should be abandoned.

• The shift toward increased sensitivity in new tests in response to the focus on early detection (in ‘treatment as prevention’ strategies) has led to inclusion of IgM detection and p24 antigen, which may increase the potential for nonspecific reactivity.

• Many repeatedly cited causes of false-positive results are based on data with limited validation or are outdated and unlikely to apply to current HIV RDTs. These include false-positive results caused by influenza vaccination, pregnancy and blood transfusion.

• Heightened CD5⁺ B-lymphocyte activation in the early immune response to infectious disease antigens produces broad-spectrum antibodies that can cause nonspecific and unpredictable cross-reactivity. High rates of false-positive immunoassay results among African patients coinfected with a variety of parasites support polyclonal B-cell activation as a cause of false positivity.

• Populations in resource-limited settings are more likely to have heightened B-lymphocyte activation than those in developed countries due to environmental factors; we propose that early B-lymphocyte response/polyspecific cross-reactivity can be a significant cause of HIV false-positive results in some settings.

• Genetic difference (higher rates of HLA polymorphism) could be another factor in some settings.

• HIV RDT results may thus vary significantly in different geographical areas and among different populations.

• Strengthening of HIV algorithms and the implementation of confirmatory testing that are feasible for use in resource-limited settings are urgent priorities.

• There is an urgent need for the development of simpler and cheaper confirmatory tests.