New HIV Testing Algorithm: A Promising Tool in the Fight Against HIV

Philip J. Peters, MD, DTM&H


March 09, 2015

Editorial Collaboration

Medscape &

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Hello, I'm Dr Phil Peters from the Division of HIV/AIDS Prevention of the Centers for Disease Control and Prevention (CDC). I would like to share an exciting development in HIV testing that will help in our fight against HIV.

HIV testing is the linchpin of prevention and treatment. For people who test HIV-positive, diagnosis opens the door to lifesaving treatment, reducing the risk of transmitting HIV to others. For those who test negative, knowing their status empowers them to remain HIV-free. Unfortunately, nearly 1 in 6 people living with HIV in the United States do not know that they have HIV, meaning that they are missing out on essential care and may unknowingly transmit the virus. In addition, diagnosing people at an early or acute phase of their HIV infection has long been one of our nation's biggest HIV prevention challenges, because these infections have eluded traditional testing technologies.

People with acute HIV infection are more likely to transmit the virus because of very high viral loads. And because antibodies have not yet developed in the acute phase, people may believe that they are HIV-negative on the basis of antibody test results. This makes early detection of acute HIV infection critical to prevention.

The good news is that healthcare providers have a powerful new tool for early detection of HIV. In June 2014, CDC recommended a new approach for HIV testing in laboratories, which capitalizes on the latest technology to improve the diagnosis of acute infection. The recommendations feature a new testing algorithm that allows the diagnosis of acute HIV infection as much as 3-4 weeks earlier than the previous testing approach.

The new algorithm begins with a combination immunoassay (also called a "fourth-generation test") that detects HIV-1 and HIV-2 antibodies and HIV-1 p24 antigen. This test is more sensitive in diagnosing early infection because it detects the HIV-1 p24 antigen, which appears before antibodies develop.

Specimens reactive on the screening fourth-generation assay are tested with a supplemental assay that differentiates HIV-1 and HIV-2 antibodies. Specimens that are reactive on the initial fourth-generation assay but nonreactive or indeterminate on the antibody differentiation assay are then tested for HIV-1 RNA to differentiate acute HIV infection from a false-positive screening result.

Laboratories using the recommended algorithm will report all of the test results separately, along with an overall interpretation. Also, note that the HIV-1 Western blot and HIV-1 immunofluorescence assay (IFA), previously recommended as the supplemental tests to diagnose HIV infection, are no longer part of the recommended algorithm.

The new algorithm can only be used with serum or plasma specimens, although rapid tests and oral fluid tests are still useful in the field when it is not possible to draw blood or when people otherwise might not be available at a later time to receive their test results. Patients with preliminary positive rapid test results can be referred for medical care and should undergo testing with a serum or plasma specimen that is tested with this new algorithm to confirm HIV infection.

To ensure that patients are tested using the new algorithm, providers should request HIV testing with the fourth-generation HIV assay, with reflex (automatic) supplemental testing—including HIV RNA testing when necessary. The new assays are increasingly available. They can be ordered at all of the large commercial labs, and many hospitals are now switching to the fourth-generation assay.

In addition to the overall earlier diagnosis of acute HIV infection, the new recommended algorithm has several advantages over previous recommendations, including more accurate laboratory diagnosis of HIV-2 infection, fewer indeterminate results, and faster turnaround time for most test results.

In conclusion, HIV testing is a proven gateway to treatment and is a key part of our prevention efforts. The new HIV testing algorithm has the potential to improve this activity in the United States. To encourage primary care providers to help ensure that all patients are tested for HIV at least once in their lives, CDC has sponsored the Act Against AIDS Initiative's HIV Screening Standard Care campaign. Please visit the Web resources about the campaign, links to the updated laboratory testing recommendations, as well as a quick guide to using the new algorithm.

Thank you for learning about the new HIV testing algorithm.

Web Resources

Laboratory Testing for the Diagnosis of HIV Infection: Updated Recommendations

CDC HIV/AIDS: Laboratory Testing

Act Against AIDS


Philip J. Peters, MD, DTM&H, is a medical officer with the Division of HIV/AIDS Prevention, US Centers for Disease Control and Prevention, in Atlanta, Georgia. Dr Peters is the activity leader for HIV testing in the Division of HIV/AIDS Prevention's Epidemiology Branch. He is responsible for conducting epidemiologic and biomedical research activities to evaluate acute HIV infection, and his professional interests include improving HIV diagnosis in the clinical setting.