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 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.
New HIV Testing Algorithm
Laboratory Testing for the Diagnosis of HIV Infection - Updated Recommendations