Quick Guide: CDC HIV Laboratory Testing Recommendations

Routine screening for HIV infection is recommended by the Centers for Disease Control and Prevention (CDC) at least once for all adolescents and adults, and more frequently for persons who engage in activities where HIV may be transmitted. This algorithm outlines the initial and confirmatory laboratory-based tests to be ordered for HIV infection screening and diagnosis.



  • Ab = antibody
  • Ag = antigen


* If suspicion of acute HIV infection or high-risk exposure within the last 2-4 weeks, check HIV RNA.

About the Tests

HIV Antigen/Antibody Combination Test

The HIV Ag/Ab combo test is an immunoassay that detects HIV in the blood by identifying either the HIV-1 p24 antigen or HIV antibodies. P24 is a viral protein which appears in the blood sooner than antibodies. This Ag/Ab test can detect HIV infection earlier than Ab-only tests, and generally a week after HIV RNA is detectable, or about 17 days after infection.

HIV-1/HIV-2 Antibody Differentiation Test

The HIV-1/HIV-2 Ab differentiation test is an immunoassay that is used both to confirm HIV infection (if the screening Ag/Ab test is positive) and to distinguish between HIV-1 and HIV-2. Results may show infection with HIV-1, HIV-2, both, or neither. Laboratory-based HIV-1, HIV-2 Ab tests can detect infection 22-25 days after infection.

HIV Nucleic Acid Test (NAT)

HIV NAT is an RNA test used to improve detection of early HIV infection. HIV-1 RNA levels are generally detectable approximately 10 days after infection. Available NAT tests in the U.S. are usually specific to HIV-1, the most common variant. HIV-2 NAT tests may be available through specialty laboratories. This test is generally considered to be too expensive to be practical for initial screening.



Modified from CDC 2014 and 2018 by John Nelson, PhD, CPNP, Susa Coffey, MD, and Nicole Mandel from the AETC National Coordinating Resource Center, February 2021.

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