Diagnostic Test Directory

Virology Laboratory

HIV-1 Western blot - serum or plasma specimen

  • Synonyms: HIV-1 Confirmatory Assay
  • LIS Mnemonic: HWB


    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 in

    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 blood specimens as soon as possible at room temperature to Central Laboratory Services. For outside clients, it is recommended that serum or plasma specimens be removed from the clot, red blood cells, or separator gel as soon as possible after collection and before shipping specimens. When shipping serum or plasma specimens, package and label specimens in complian


    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. If


    An HIV-1 Western blot is automatically ordered on all specimens that test repeatedy reactive for HIV-1/HIV-2 by the 4th generation antigen/antibody screening immunoassay in order to confirm the results.

    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 boody fluids other than human serum or plasma.

    Specimen Handling

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

Days Performed

Tuesday-Wednesday (Requires 2 days to complete)


1 week

Reflex Testing





Immunoblot Assay

Disease Information


The Western blot procedure has been widely accepted as a confirmatory method for HIV antibody. It is intended for use as an additional, more specific test for HIV-1 antibodies in persons of unknown risk whose serum or plasma specimens have been found to be repeatedly reactive using screening procedures such as an enzyme immunoassay. In the U.S., Western blotting is usually performed for confirmation of antibodies specific to HIV-1 since the prevalence of HIV-2 infection is low. HIV-2 specific Western blots are not routine done, but are normally available from commercial reference laboratories.


POSITIVE: A specimen that is positive/reactive in both the antigen/antibody screening test and the Western blot is presumed to be positive for antibo

Reference Values

NONREACTIVE or negative by Western blot procedure for antibody to HIV-1

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