New HIV Testing Strategy Recommended for Earlier, Accurate Diagnosis
Early, acute HIV infections contribute disproportionately to the spread of the virus and are the source of a substantial number of new infections, according to the Centers for Disease Control and Prevention (CDC). During the acute stage, the level of the virus is very high. Many people are unaware that they are infected and unknowingly pass the virus on to others.
Now, public health officials from the CDC and the Association of Public Health Laboratories (APHL) have jointly endorsed the use of a new HIV testing strategy, also called an algorithm, that aims to make HIV diagnoses earlier in the course of the disease and decrease the rate of transmissions from acute infections. The new recommendations were released June 27, 2014 in time to mark the 20th annual National HIV Testing Day.
Use of the new algorithm will lead to HIV diagnosis as much as 3 to 4 weeks sooner than the previously recommended testing approach that was introduced in 1989. Earlier diagnosis will allow people who are infected to take advantage of treatment options sooner and take steps to avoid transmitting the virus.
Two studies published in a report by the CDC late last year showed that more acute infections were detected using the new testing strategy than the traditional approach. (See the article New HIV Testing Strategy Improves Detection of Early, Acute Infections, Studies Find). The new recommendations are based on those studies as well as other "scientific evidence, laboratory experience, and expert opinion" collected from 2007 through December 2013, according to the CDC.
The new algorithm takes advantage of innovative technology and tests that have been recently approved by the Food and Drug Administration. It includes the following steps:
- Initial screening uses newer combination blood tests that can identify early as well as late infections by simultaneously testing for an HIV antigen called p24 and HIV antibody. Most tests that are currently in use only detect HIV antibody and not p24.
- The level of p24 antigen increases significantly in the blood soon after initial infection (as early as 10-14 days after initial infection with HIV virus). Thus, testing for p24 allows for earlier identification of infections.
- As the disease progresses, the level of p24 declines. About 2-8 weeks after exposure, antibodies to HIV are produced in response to the infection and remain detectable in the blood thereafter. Testing for HIV antibody ensures that infections can be detected later in the course of disease.
If the combination test is negative, no further testing is required.
- If the combination test is positive, a second test is done that differentiates between two types of antibodies to different forms of the virus, HIV-1 and HIV-2. A positive on this test confirms the presence of HIV antibodies and the diagnosis of HIV-1 or HIV-2.
- If the second test is negative or indeterminate, it may mean that the infection is acute and HIV antibodies have not yet developed. A molecular test that detects the genetic material (nucleic acid) of the virus is performed. A positive confirms a diagnosis while a negative result indicates a false-positive on initial testing.
(Each of these tests can be performed on the same sample of blood. This testing sequence usually does not require that multiple blood samples be drawn.)
"Identifying acute infections has long been one of our nation's biggest HIV prevention challenges, since these infections eluded traditional testing technologies. But with consistent and widespread use of this new testing method, we can diagnose people several weeks earlier than before. CDC is supporting laboratories to adopt this new approach as quickly as possible," said Jonathan Mermin, MD, MPH, director of the CDC's National Center for HIV/AIDS, Viral Hepatitis, STD, and TB Prevention.
It may take some time for the combination tests to become more widely available and for health practitioners and laboratories to adopt the new algorithm. Meanwhile, individuals who think that they may have been exposed, whether recently or in the past, or who are at high risk for HIV infection may wish to talk to their health practitioner about their testing options and these new recommendations. Questions to ask may include:
- Which screening test is available and does it detect HIV antibody or both p24 and the antibody?
- How long after initial infection does it take for the test to show a positive?
- How will results be evaluated and will I need follow-up testing?