HIV antigen/antibody combo screening assay - serum specimen

Collect

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 plastic tubes containing lithium heparin with gel separator, sodium heparin, dipotassium EDTA with or without gel separator, and glass tubes containing tripotassium EDTA or disodium EDTA.

Volume Required

4 ml of blood

Minimum Required

2 ml of blood

Transport

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, and international regulations covering the transport of clinical specimens and infectious substances. Specimens may be shipped at 2-8C (wet ice) or frozen (dry ice). Do not exceed the storage time limitations listed under the heading of Stability.



Stability

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 a storage period greater than 7 days is anticipated, serum or plasma should be stored frozen at -20C or colder. No more than 5 freeze-thaw cycles should be performed on any sample prior to testing, and specimens should not be stored in frost-free freezers.

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. One should remove the serum or plasma from clotted blood, red blood cells, or separator gel as soon as possible to avoid hemolysis. The best results are generally observed for serum or plasma specimens that are clear and nonhemolyzed. Lipemic, icteric, or hemolyzed specimens should be avoided when possible, and specimens with obvious microbial contamination should not be used. Specimens containing unremoved clots, red blood cells, or particulate matter may give inconsistent results and should be clarified by centrifugation before testing.

Days Performed

Monday thru Friday

Reported

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.

CPT

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

Methodology

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

Utility:

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 antibodies to HIV is presumed to be infected with the virus; however, an individual who has participated in an HIV vaccine study may develop antibodies to the vaccine and may or may not be infected with HIV. Clinical correlation is indicated with appropriate counseling, medical evaluation, and possibly additional testing to determine whether a diagnosis of HIV infection is accurate.

A test result that is nonreactive does not exclude the possibility of exposure to or infection with HIV-1 and/or HIV-2. Nonreactive results in this assay for individuals with prior exposure to HIV-1 and/or HIV-2 may be due to antigen and antibody levels that are below the limit of detection of this assay.

The performance of this assay has not been established for individuals younger than 2 years of age. Nearly all infants born to HIV-infected mothers passively acquire maternal antibody and, in some cases, will test antibody positive until age 18 months regardless of whether they are
infected. Definitive diagnosis of HIV infection in early infancy requires other assays, including molecular amplification assays for HIV nucleic acid.

Interpretation

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 p24 antigen and/or HIV-1/HIV-2 antibodies; perform supplemental confirmatory assay(s).

All specimens that are initially reactive must be centrifuged and retested in duplicate before results are finalized. If one or both repeat tests are REACTIVE (e.g., S/CO > or = 1.00), the final result is consdered to be REPEATEDLY REACTIVE for HIV-1 p24 antigen and/or HIV-1/HIV-2 antibodies by the HIV Ag/Ab Combo Assay.

A reactive result using the HIV Ag/Ab Combo Assay does not distinguish between the detection of HIV-1 p24 antigen, HIV-1 antibody, or HIV-2 antibody.

Reference Values

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

Remarks

As of 15 May 2012, written informed consent for HIV testing is no longer required; documentation of verbal consent is adequate. Our hospital policies have been modified to conform with the revised Pennsylvania Act 148 (state statute that governs HIV testing) and the emphasis of the Commonwealth of Pennsylvania and Centers for Diseases Control and Prevention to provide routine HIV testing of individuals 13-65 years of age. This policy change applies to CHOP affiliated inpatient and outpatient care sites in Pennsylvania, New Jersey and Delaware. The new HIV-related policies can be found in the online Patient Care Manual. The patient or person consenting to the test must still be notified of the intent to test and be provided with HIV-related information. Two handouts are available in the Patient-Family Education Manual to provide information about HIV and HIV testing: "Understanding HIV: Testing and Prevention" and "HIV Testing is for Everyone". A competent minor, regardless of age, is permitted under Pennsylvania state law to consent to HIV testing and/or treatment services. Parental consent is not required. Otherwise, verbal consent can be obtained only from a biologic parent, an adoptive parent, legal guardian, or by a court order. Documentation in the medical record must show that verbal consent was obtained. Documentation of verbal consent for an HIV-related test can be accomplished through the Epic hospital computer system by selecting one of two certifications; either "I certify that the patient and/or personal representative have been given information about HIV testing and have verbally consented to the test" OR "I certify that HIV testing is required because of a life threatening medical condition or occupational exposure, and obtaining consent is not possible at this time".