False positive HIV tests: the problem no one wants to talk about (and how to solve it)

By PLoS Guest Blogger

Guest post by Leslie Shanks of MSF, the second of three guest posts from the 2011 ICASA conference in Addis Ababa. The International Conference on HIV/AIDS and Sexually Transmitted Infections in Africa (ICASA) is the principal forum on HIV/AIDS & STIs in Africa.

“Finally, someone is talking about this.” I heard this refrain frequently at the recent ICASA conference in Addis-Ababa, Ethiopia after telling people about the satellite session hosted by Doctors Without Borders/Médecins Sans Frontières (MSF). The difficult topic: false positive HIV tests.

In resource-limited settings, HIV diagnosis is done with rapid diagnosis tests (RDT) using two or three different RDTs in either a serial or parallel algorithm (according to national guidelines). Rapid tests allow scale up and decentralization of treatment, both of which are essential to saving lives. Yet RDTS are screening tests –they were not designed for definitive diagnosis [1]. They work well for screening blood transfusions and identifying people who need further tests, but are known to yield false positive results due to serological cross-reactivity (or to inadequate quality control and human error (e.g. mislabeling of specimens). I first came across this unpleasant reality in Bukavu, DRC while working as a medical coordinator for MSF in 2005. We were running the first program offering ART to the province and had tested nearly 6000 people. But late in 2004 we came to realize that some people in our program did not have HIV, so we re-tested a number of them—and identified almost 50 who were suspect for false positive HIV diagnosis. This news was devastating, considering the consequences a false diagnosis can have on people’s lives.

We immediately worked to put stricter quality control protocols in place to eliminate errors in the testing process, and we reviewed all aspects of the program. Then we piloted a confirmation test for people who screen positive on two RDTs, using a test that is simple to use and interpret, requires no special equipment, and yields results in less than two hours [2] . All patients with a suspected false diagnosis were counseled and re-tested using the confirmation test. The reaction of those identified as false-positive varied. One woman said that her husband had divorced her, and she had remarried someone from the HIV+ peer support group. A pastor was immensely relieved to hear that he was HIV-negative, since he could never figure out how he got infected. Some felt it was a miracle from God, or evidence that the latest magic potion on the market cured HIV. Since people in the community were dying from lack of access to testing, we were very concerned about the potential consequences if people lost confidence in the testing program. But in fact we saw no decrease in uptake of testing or loss of confidence in our program. In fact, we learned that many local people were encouraged to come to MSF for testing due to the additional guarantees our program introduced.

At the MSF satellite session on HIV testing, we presented an interim analysis of our data from Ethiopia. The 2 study sites initially showed a 7% false positive rate using the national algorithm, which relies on 2 out of 3 positive tests (“tie-breaker” algorithm). Using an improved algorithm (with the confirmation test) the number of false positives dropped to zero. The UNHCR (UN Refugee Agency) presented its experience in Uganda: after recognizing problems with testing in its PMTCT programs, they adopted new measures to improve quality control and accuracy of the tests. Audience members shared similar experiences from their programs in several countries. Many spoke of policy makers’ reluctance to allow re-testing of people already under care, even if a problem with false positives was identified, or to openly acknowledge the issue.

Given the vital importance of testing and getting people on life-saving treatment, these testing problems are arguably outweighed by the greater good RDTs bring for scaling up access to care. However, it’s not either-or: there are feasible solutions that virtually eliminate the problem, such as improving the test algorithm, adding a simple confirmation test, and improving quality control.
In this era of initiating treatment earlier and scaling up community and door-to-door testing, confidence in the test algorithms is more important than ever. Fortunately for those still waiting to be tested, there are good solutions. It’s just a matter of putting them in place.

Leslie Shanks is a Canadian physician working for Médecins sans Frontières since 1994. She currently works in the position of Medical Director based in Amsterdam.

The author has completed the ICMJE uniform disclosure form at www.icmje.org/coi_disclosure.pdf (available on request from the corresponding author) and declares: no support from any organisation for the submitted work; no financial relationships with any organisations that might have an interest in the submitted work in the previous three years, no other relationships or activities that could appear to have influenced the submitted work.

[1]  Greenwald JL, Burstein GR, Pincus J, Branson B. A Rapid Review of Rapid HIV
Antibody Tests. Curr Infect Dis Rep. 2006 Mar;8(2):125-31

[2]  Klarkowski, D.B et al. The evaluation of a rapid in situ HIV confirmation test in a program with a high failure rate of the WHO HIV two test diagnostic algorithm. PLoS ONE February 2009 4 (2): e4351