HIV-1 Western blot - serum specimen
- LIS Mnemonic: HWB
Collect
Gold (SST - Clot activator & gel)
Volume Required
2 ml blood
Minimum Required
1 ml serum
Transport
A total of 2-4 ml of blood (for every 2-3 HIV and Hepatitis tests ordered) should be collected and submitted at room temperature to the laboratory.
Stability
N/A
Processing
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.
Days Performed
Tuesday-Wednesday (Requires 2 days to complete)
Reported
1 week
Reflex Testing
N/A
CPT
86689
Methodology
Immunoblot Assay
Disease Information
Utility:
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.
Interpretation
POSITIVE: A specimen that is positive/reactive in both the antigen/antibody screening test and the Western blot is presumed to be positive for antibody to HIV-1, indicating infection with this virus. Notable exceptions include situations of passively-acquired (e.g., mother-to-fetus) antibody or experimental vaccination. Antibodies to HIV-2 may also cross-react with the proteins of HIV-1 used in the Western blot. Therefore, individuals infected with HIV-2 may have reactive tests in the HIV-1 Western blot. Usually, however, the cross-reactivity is incomplete and results in an indeterminate test. Individuals with positive test results should be referred for medical evaluation.
NEGATIVE: A negative Western blot result suggests, but does not completely prove, that the person has not been exposed to HIV-1. However, such findings may provide useful information in the context of medical evaluation for which clinical information is available. Additional testing is normally warranted.
INDETERMINATE: Indeterminate Western blot results mean that the detection of antibodies to HIV-1 can neither be confirmed or ruled out and such results should not be used as the basis for diagnosis of HIV-1 infections. Reasons for indeterminate Western blots include (1) early seroconversion, (2) loss of antibody responses in patients with late-stage AIDS, (3) seroreversion in uninfected infants with maternal antibody, (4) HIV-2 infection, and (5) failure to mount an adequate immune response. Due to the uncertainty associated with indeterminate Western blots, additional testing is recommended.
Reference Values
NONREACTIVE or negative by Western blot procedure for antibody to HIV-1
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".
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