NEW YORK – The National Institutes of Health said Tuesday that a study has found that a single HIV viral load test that is used in the US may generate false positive results in patients who are receiving long-acting injectable cabotegravir (CAB-LA) for HIV pre-exposure prophylaxis.
The researchers determined that performing a second confirmatory test raised the positive predictive value to 100 percent, however.
CAB-LA is administered by injection every two months, and both the US Food and Drug Administration and US Centers for Disease Control and Prevention recommend that people who take the drug submit to routine lab-based HIV viral load tests.
The NIH said that study results presented this month at the 2024 International AIDS Conference in Munich indicate that a single viral load test had a 9.1 percent positive predictive value in patients who had received a CAB-LA injection within the past six months.
The finding, the NIH said, suggests that the single test HIV viral load test "did not reliably detect HIV."
The test had a 60 percent positive predictive value in patients who were off CAB-LA for more than six months.
The positive predictive value increased to 100 percent with a second viral load test that was performed on a new blood sample, the NIH said. The research, which followed 2,620 men who have sex with men and transgender women who have sex with men, was an extension of a prior study into the performance of long-acting injectable PrEP in comparison with daily oral PrEP.
Jeanne Marrazzo, director of the NIH National Institute of Allergy and Infectious Diseases, said in a statement that healthcare experts are still learning how to optimize HIV testing and other services that are used along with long-acting PrEP.
“The viral load testing findings observed in this study illuminate performance gaps in the current US HIV testing algorithm for injectable cabotegravir PrEP," she said.
The NIH noted that previous research also showed that combinations of two antibody-based HIV tests performed with between 83 percent and 100 percent positive predictive values in patients who were receiving CAB-LA.