HIV testing has improved dramatically since the first generation of tests came out in the 1980s. Then, patients exposed to the virus had to wait months for markers to reach detectable levels. A positive screening result often meant a return visit for further testing.
Subsequent test generations have reduced the detection window considerably and sped up results. Fourth-generation HIV tests, which have been on the market in the United States since 2010, have a detection window of just 2 to 4 weeks. In 2014, the U.S. Centers for Disease Control and Prevention (CDC) updated its HIV testing algorithm to encourage laboratories to adopt the newer tests and migrate away from Western blot for confirmatory testing.
Today, clinical labs are still on the front lines of ensuring proper screening for HIV as well as the best treatment for patients who are HIV-positive. With a push for ever broader screening, and ongoing technological breakthroughs from test manufacturers, labs are at the center of change, and rapid, point-of-care (POC) molecular testing for HIV may soon be on the horizon.
Faster Turnaround, Earlier Detection
Monica Parker, PhD, chief of the bloodborne diseases laboratory at the New York State Department of Health’s Wadsworth Center, said the 2014 CDC algorithm has been working well in her lab. The algorithm calls for an HIV 1/2 antigen/antibody combination immunoassay (i.e., a fourth-generation test) for screening. Positive results are confirmed with an HIV1/HIV2 antibody differentiation immunoassay. If antibodies do not confirm as positive on this supplemental test, a nucleic acid test is used to determine whether the patient has an acute infection—antigen present but no antibodies—or the screening result was a false positive.
Parker’s laboratory was involved in collecting some of the data that CDC used to support the new algorithm, and has been using some of the new tests since before the algorithm was officially recommended. “I’ve seen two major improvements related to implementing that algorithm,” Parker said. “One is the turnaround time for results has been greatly reduced in most cases.”
Previously, samples had to be batched for Western blot confirmatory tests so the tests were not run every day, she said. The new supplementary tests can be run on single samples, and they give a result in less than 30 minutes, allowing the lab to return results within a day in most cases. “The other improvement that we have seen is that quite often infections are being detected and confirmed earlier,” she said. Her laboratory also runs the entire testing algorithm on a single sample, reducing the need to track down patients for repeat testing, she added. “It has probably reduced the amount of overall testing that people need to go through in order to get their HIV status confirmed,” Parker said.
The algorithm also appears to be working at Zuckerberg San Francisco General Hospital and Trauma Center. A new study found the algorithm performed just as well as the hospital’s previous strategy, said co-author Christopher Pilcher, MD, a professor at the University of California San Francisco School of Medicine (J Clin Virol 2017;91:73–8).
One notable change with the new algorithm, Pilcher said, was an increase in false positives due to the sensitivity of fourth-generation screening tests, and the subsequent wait for viral load testing for definitive answers. “The fact that the majority of results were false positives meant that it caused a lot of anxiety among clinicians,” he said.
New POC molecular instruments could help solve that problem, he said. “We urgently need to have a POC viral load test, or at least a rapid-turnaround, random-access type of viral load test, available so that laboratories can do immediate confirmation,” Pilcher said.
Parker agreed on the need for POC viral load testing. “I think that is the thing that all of us are waiting for,” she said. “If you can get those results back to those individuals, even while they’re still on site, you have a much better chance of getting them into the care system.”
However, the cost of POC viral load testing will be justified only in certain populations, cautioned William Clarke, PhD, director of clinical toxicology and the critical and point-of-care testing program at the Johns Hopkins Hospital in Baltimore. POC viral load testing would help patients who could be lost to follow-up, Clarke said, but “if there’s more of a routine population, where you know they’re either aware that they’re at risk or they’re motivated or they’re interested to find out their HIV status, it’s not going to be a problem to get them back a week or two later.”
Large clinics that see many at-risk patients, though, are eager for faster definitive results on site. Some clinics are considering setting up their own laboratories capable of moderate-complexity testing so they will be able to offer the Bio-Rad Geenius supplemental tests on site, Pilcher said. When POC viral load tests reach the market, patients could get results very quickly.
“You can imagine that whole algorithm taking place in two hours, so you could get somebody in and out in the same visit,” Pilcher said. “That would be really exciting. I think that’s where things are going.”
Expanding the Reach of HIV Testing
As HIV diagnostics improve, laboratorians are leading the effort to expand testing by implementing opt-out screening programs. Opt-out programs, which have been recommended by CDC since 2006, seek to remove the stigma of HIV testing by offering it to all patients as part of routine care, regardless of risk factors and without requiring special written consent or counseling. “It has resulted in significantly higher rates of uptake of testing by patients and identification of a lot of patients with unrecognized HIV who otherwise may not have been tested,” said Richard E. Rothman, MD, PhD, professor and vice-chair of research at the Johns Hopkins Medicine Department of Emergency Medicine in Baltimore.
Expanded screening benefits not only individual patients, but also the community because patients who know they have HIV are less likely to spread the virus, according to Rothman. “You can make a major difference to the health of the population and the cost to the hospital by getting people diagnosed early,” he said.
While opt-out programs were first adopted at major metropolitan healthcare systems, they are now reaching beyond cities. West Virginia University Hospitals, for example, just joined with Gilead Sciences’ FOCUS Program this year to bring opt-out HIV and hepatitis C screening to its patients in rural Appalachia. “They approached us because in Appalachia we have a large population of chronic drug users,” said Danyel Tacker, PhD, the hospital system’s director of chemistry and mass spectrometry in Morgantown. “We probably have a prevalence of infectious diseases that we’ve been underestimating for years simply because we’re not testing universally.”
Expanding testing across multiple departments and hospitals has not been easy, Tacker emphasized. “The big challenges for us were lining up what testing to use, what algorithm to use,” she said. Yet Tacker and her colleagues are making it work. “Even if you’re a small hospital, even if you’re at a small site, this is not something that you should sideline,” she said. “It’s a universal issue. It’s something that everybody needs to think about partnering in.”
Challenges for Laboratories
As HIV testing improves and expands, new challenges arise for laboratories. In some cases, even the 2014 CDC algorithm is starting to feel outdated. For example, Bio-Rad’s BioPlex 2200 HIV Ag-Ab kit is marketed as a fifth-generation screening test because it both detects and differentiates HIV analytes. “It’s unclear to labs how they’re supposed to use it, what they’re supposed to confirm it with,” Pilcher said. “Are they supposed to do another HIV1/HIV2 differentiation assay? How do you interpret those results if they are discrepant?”
Also, unexpected test results arise as patients are diagnosed earlier, he said. For example, patients who are diagnosed with acute HIV infection and treated immediately may not develop antibodies in the usual pattern. After several months of treatment, many of them will test negative for HIV antigen and antibody, though they are still infected. “If these patients go to their local doctors, the doctor is going to test them and say they’re HIV-negative,” Pilcher said. “No matter what test you do, nobody’s going to be able to document that they’re HIV infected, and there are going to be all kinds of questions.”
Laboratorians and physicians also should know that preexposure prophylaxis (PrEP) can affect test results, particularly if a person becomes infected with HIV during a lapse in PrEP medication. PrEP sometimes interferes with the usual antibody and antigen responses and reduced viral load, leading to negative or conflicting test results. However, Pilcher doesn’t see this as a negative. “It’s not a problem, because it’s a good thing,” he said, adding that these kind of issues are the result of improved patient care and progress toward ending the HIV epidemic, and it’s worth all the work that laboratories and physicians have to put in as technology changes, he said.
Julie Kirkwood is a freelance journalist who lives in Rochester, New York. +Email: [email protected]