New CDC HIV Testing Recommendations Offer Faster Diagnosis

Megan Brooks

June 26, 2014

Ahead of National HIV Testing Day on June 27, the Centers for Disease Control and Prevention (CDC) is recommending a new approach for HIV testing in laboratories.

The new approach "capitalizes on the latest technology to improve diagnosis of acute infection, the earliest stage of HIV infection when people are most likely to transmit the virus," Jonathan Mermin, MD, MPH, director of the CDC's National Center for HIV/AIDS, Viral Hepatitis, STD, and TB Prevention, said in a statement.

Adopting the new recommendations will lead to HIV diagnosis as much as 3 to 4 weeks sooner than the previous testing approach, the CDC says.

"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," Dr. Mermin said.

Acute and early infection can account for 10% to 50% of all new HIV-1 transmissions, according to the CDC. Extremely high levels of infectious virus can persist for 10 to 12 weeks during the acute phase.

Sequence of Tests

The new recommendations advise a sequence of tests used in combination, starting with a fourth-generation HIV test (step 1).

"This will detect HIV in the blood earlier than previously recommended antibody tests by identifying the HIV-1 p24 antigen, a viral protein which appears in the blood sooner than antibodies," the CDC says.

If this initial test is negative, no further testing is needed.

If it is positive, then obtain an immunoassay that differentiates HIV-1 from HIV-2 antibodies (step 2). These assays produce results faster than the previously recommended Western blot and distinguish between HIV-1 and HIV-2, which the previously recommended Western blot cannot do. This distinction can have "important treatment implications for a patient," the CDC notes.

The HIV-1 Western blot and HIV-1 immunofluorescence assay, previously recommended to make a laboratory diagnosis of HIV-1 infection, are no longer part of the recommended algorithm.

In the face of a positive result on the initial immunoassay but negative or indeterminate result on the antibody differentiation assay, the CDC advises proceeding to HIV-1 nucleic acid testing for resolution (step 3). This "ensures accurate detection of early infection or indicates a false positive from the fourth generation test," the CDC says.

"The results of this algorithm may be used to identify persons likely to benefit from treatment, to reassure persons who are uninfected, and for reporting evidence of HIV infection to public health authorities," the CDC says.

Testing the "Linchpin" for Prevention, Treatment

The new recommendations are based on both HIV tests approved by the US Food and Drug Administration (FDA) as of December 2012 and "scientific evidence, laboratory experience, and expert opinion" collected from 2007 through December 2013, the CDC says.

"These recommendations do not include the rapid HIV-1/HIV-2 antigen/antibody combination test approved by the FDA in August 2013 (for which evidence of performance in the algorithm was insufficient) or HIV-2 nucleic acid tests...which lack FDA approval," they note.

Although HIV testing is the "linchpin" for prevention and treatment, more than half of American adults still have never been tested, Dr. Mermin notes in a statement.

"Nearly 1 in 6 people living with HIV in the United States do not know they have HIV, meaning that they are missing out on essential care and may unknowingly transmit the virus. Roughly half of the estimated 50,000 new HIV infections each year are transmitted by people who don't know that they are HIV-positive," Dr. Mermin adds.

However, the United States is making "steady progress" on HIV testing, he said. Since the CDC recommended HIV testing for all Americans aged 13 to 64 years in 2006, the proportion of people who are unaware of their HIV infection has declined steadily, from roughly 20% to 16%. The new recommendations "could help the nation reduce that number further," Dr. Mermin said.

"Laboratory Testing for the Diagnosis of HIV Infection: Updated Recommendations." CDC. Published June 27, 2014. Full text


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