Diagnostic Test Directory

Virology Laboratory

HIV antigen/antibody combo screening assay - serum or plasma specimen

  • Synonyms: HIV screen, HIV antibody, HIV antigen, HIV antigen/antibody combo
  • LIS Mnemonic: HIV AG/AB


    PREFERRED: Serum is the preferred specimen. Collect blood in a 4 ml Gold Serum Separator Tube-Clot Activator & Gel. REMARK: Plasma is an acceptable alternative specimen. Blood can be collected i

    Volume Required

    4 ml of blood

    Minimum Required

    2 ml of blood


    A total of 2-4 ml of blood (for every 2-3 HIV and Hepatitis tests ordered) should be collected. For the CHOP enterprise, submit specimens as soon as possible at room temperature to Central Laboratory Services. For outside clients, it is recommended that specimens be removed from the clot, red blood cells, or separator gel as soon as possible after collection and before shipping specimens. When shipping specimens, package and label specimens in compliance with applicable state, federal, an


    Serum or plasma specimens should be stored for no longer than 3 days at room temperature or 7 days at 2-8C following specimen collection and separation from clot, red blood cells, or separator gel. I

    Unacceptable conditions

    Do not use serum or plasma specimens that are heat-inactivated, pooled, grossly hemolyzed, or contain obvious microbial contamination. Performance has not been established for the use of cadeveric specimens or the use of boody fluids other than human serum or plasma.

    Specimen Handling

    Unprocessed blood specimens should routinely be refrigerated at 4C upon arrival in the laboratory.

Days Performed

Monday thru Friday


1-3 days

Reflex Testing

If testing is positive, supplemental confirmatory testing (e.g., Western blot and RNA qualitative test) is performed. Refer to these tests in the Online Lab Service Directory for additional information.


86703 (initial screening), 86689 (Western blot), 87535 (RNA qualitative test)


Chemiluminescent microparticle immunoassay (CMIA) for the simultaneous qualitative detection of HIV-1 p24 antigen, antibodies to HIV-1 (groups M and O), and antibodies to HIV-2.

Disease Information


The HIV Ag/Ab Combo Assay is the first assay to detect both antigen and antibodies to HIV. This assay is licensed by the FDA for use as an aid in the diagnosis of HIV-1/HIV-2 infection, including acute or primary HIV-1 infection, in adults (including pregnant women), and in children as young as two years old. Since the assay can directly detect HIV-1 (specifically the p24 Ag of the virus), it can be used to improve the early diagnosis of HIV-1 infection prior to the emergence of specific antibodies. The HIV Ag/Ab Combo Assay is not intended for use in screening blood or plasma donors. However, this assay can be used as a blood donor screening assay in urgent situations where traditional licensed blood donor screening tests are unavailable or their use is impractical. The interpretation of specimens with a final result of reactive by the HIV Ag/Ab Combo assay and indeterminate by supplemental confirmatory Western blot is not definitive; further clarification may be obtained by testing another specimen taken at least 1 month later or performing molecular-based assays that directly target viral nucleic acid. The HIV Ag/Ab Combo assay result and supplemental confirmatory assay results should be interpreted in conjunction with the patient’s clinical presentation, history, and other laboratory results. If the results are inconsistent with clinical evidence, additional testing is suggested to confirm the result. Please call the laboratory. An individual who has antibod


S/CO <1.00 NONREACTIVE - No detection of HIV-1 p24 antigen and HIV-1/HIV-2 antibodies. S/CO > or = 1.00 REACTIVE - Presumptive evidence of HIV-1 p2

Reference Values

S/CO <1.00 NONREACTIVE for HIV-1 p24 antigen and/or HIV-1/HIV-2 antibodies

Search Lab Test Directory

Search by disease or test name

View a full list of all lab tests

Contact Us

Ask for more information about our laboratory services.