A false positive result from an isolated viral load may be generated for people using PrEP with long-acting treatment.

Press release

Tuesday July 23, 2020

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Results from a large NIH-funded study provide new insights into the clinical utility of current testing algorithms in the United States.

Color transmission electron micrograph of HIV-1 particles (blue) budding and multiplying from an H9 cell (bright green). The shape of the viral particles is due to the different stages of maturation.NIAID

In a multi-country study, a single laboratory HIV viral load test performed by U.S. physicians prescribing long-acting injectable CAB-LA for HIV pre-exposure prophylaxis (PrEP) did not reliably detect HIV. A single positive viral load test result was often a false positive in the study. However, a second viral test using a fresh blood sample was able to distinguish true-positive results from false-positive results in all participants with a positive viral load. These results were reported at the 2024 International AIDS Conference in Munich, Germany.

Jeanne Marrazzo MDMPH is the director of NIAID, the National Institute of Allergy and Infectious Diseases of the National Institutes of Health (NIH). The viral load test results observed in this research highlight gaps in the performance of the U.S. HIV testing algorithm for injectable cabotegravir PreEP.

CAB-LA is a long-acting injectable PrEP based on cabotegravir. Highly effective HIV prevention methodIt is given intramuscularly every two months. PrEP is not recommended without routine HIV monitoring to ensure that users are aware of any HIV infections while on PrEP. In the United States, people taking PrEP must have their HIV status routinely monitored. This is done so that they can be informed immediately if they acquire HIV while taking PrEP medications. Oral PrEP You can test for HIV using lab-based HIV tests or self-tests and rapid point-of-care tests. The FDA and CDC recommend that those who start CAB-LA PrEP or have been taking it for a while get a viral lab test. Detects HIV genetic material In the blood. The recommendation was given because CAB LA can keep HIV antibodies so low that they may not show up in antibody-based tests. Researchers looked at viral load results to better inform the US CAB LA PrEP HIV testing algorithm. This was done as part of an open-label extension of a CAB LA PrEP efficacy trial.

The open-label extension of the study followed 2,620 men, gay and bisexual men, and transgender women who had sexual intercourse. From the original study sample. 29 participants acquired HIV during the study extension. Five of the 29 participants (17.2 %) were diagnosed with HIV for the first time following a single positive viral load result. Two of these five participants had been on CAB LA in the past six months while three others had not been on CAB LA for more than six months. Twenty-four participants tested positive for HIV on multiple occasions. Some 23 participants also had a single positive viral load result, but 22 of these were negative on confirmatory testing, meaning their initial result was false. One person's status could not be established at the time the test was performed.

The data show that a single positive viral test had a positive predictive validity of 9.1% – that is, a 9.1% probability of being a true HIV infection rather than a false positive – among study participants who received their last CABLA injection within the past six months. A positive predictive accuracy of 60 % was found for participants whose CABLA injections were more than six months old. The positive predictive value of a single viral load test increased from 9.1 % to 100 % among participants who received a CAB-LA injection within the past six months. This was true regardless of when the participant’s CAB-LA shot occurred.

A false positive could lead to PrEP interruptions, which could create vulnerability to HIV infection, but more importantly, it could cause profound psychological distress in the patient waiting for confirmation from the second test, said Raphael Landovitz, professor of medicine at the University of Toronto David Geffen School of Medicine at the University of California, Los Angeles. Those concerns must be weighed against the benefits that might come from a slightly earlier HIV diagnosis.

In previous analyses, this study found that combinations of two antibody-based tests had positive predictive values ranging from 83 to 100% for participants taking CAB-LA PreP. These findings, the authors say, fill the evidence gap regarding the performance of available HIV testing tools to optimize CAB LA PrEP implementation. These global CAB-LA studies, supported by NIAID, continue to influence HIV prevention policy and practice.

NIAID is supporting this open-label extension study in collaboration with ViiV Healthcare, Gilead Sciences, Inc., and the NIH-funded HIV Prevention Trials Network. HPTN, in collaboration with NIAID and ViiV Healthcare, is conducting the HPTN-funded trial. ViiV Healthcare, Gilead Sciences, Inc., and HPTN are providing the study drug. The NIH National Institute of Mental Health and the NIH National Institute on Drug Abuse are the study drug providers. Eunice Kennedy Shriver This study was conducted in collaboration with the National Institute of Child Health and Human Development and NIAID.

ClinicalTrials.gov has more information about the HPTN 083 study under the identifier NCT02720094.

NIAID supports and conducts research at NIH, in the United States, and around the world to study and develop new methods for diagnosing, preventing, and treating infectious and immune-mediated diseases. On the NIAID website, you can find news releases, fact sheets, and other NIAID materials. NIAID website.

The National Institutes of Health: NIH is the medical research agency of the U.S. Department of Health and Human Services. It includes 27 institutes and centers. NIH, the National Medical Research Agency, is one of the federal agencies that conducts and supports basic, translational, and clinical medical research. It also studies the causes, treatments, and cures for common and rare diseases. Visit NIH for more information about its programs and services. www.nih.gov.

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