HIV-1 and HIV-2 Antibody Differentiation, Serum
Clinical Information Discusses physiology, pathophysiology, and general clinical aspects, as they relate to a laboratory test
AIDS is caused by 2 known types of HIV. HIV type 1 (HIV-1) is found in patients with AIDS, AIDS-related complex, and asymptomatic infected individuals at high risk for AIDS. The virus is transmitted by sexual contact, by exposure to infected blood or blood products, or from an infected mother to her fetus or infant. HIV type 2 (HIV-2) infection is endemic only in West Africa, and it has been identified in individuals who had sexual relations with individuals from that geographic region. HIV-2 is similar to HIV-1 in viral morphology, overall genomic structure, and its ability to cause AIDS.
Antibodies against HIV-1 and HIV-2 are usually not detectable until 6 to 12 weeks following exposure and are almost always detectable by 12 months. They may fall to undetectable levels (ie, seroreversion) in the terminal stage of AIDS when the patient's immune system is severely depressed.
Routine serologic screening of patients at risk for HIV-1 or HIV-2 infection usually begins with a HIV-1/-2 antigen and/or antibody screening test, which may be performed by various FDA-approved assay methods, including rapid HIV antibody tests, enzyme immunoassays, chemiluminescent immunoassays. In testing algorithms that begin with these methods, supplemental or confirmatory testing should be requested only for specimens that are repeatedly reactive by these methods according to assay manufacturers' instructions for use.
Detection and differentiation of HIV-1 and HIV-2 antibodies
Supplemental testing of specimens that are reactive by FDA-approved HIV-1/-2 antigen and antibody combination tests
Negative results for both HIV-1 and HIV-1 antibodies usually indicate absence of HIV-1 and HIV-2 infection. However, such negative results do not rule out acute HIV infection. If acute HIV-1 infection is suspected, detection of HIV-1 RNA (HIVQU / HIV-1 RNA Quantification, Plasma) or HIV proviral DNA (PHIV / HIV-1 Proviral DNA Qualitative Detection by PCR, Blood) is recommended.
Positive HIV-1 antibody but negative HIV-2 antibody results suggest the presence of HIV-1 infection. Together with the reactive HIV-1/-2 antigen and antibody screening test results, individuals with such results are considered presumptively positive for HIV-1 infection. Additional testing for HIV-1 RNA (HIVQU / HIV-1 RNA Quantification, Plasma) is recommended to verify and confirm the diagnosis for consideration of antiviral treatment.
Indeterminate HIV-1 antibody but negative HIV-2 antibody results may be due to early HIV-1 infection, cross-reactive antibodies produced from recent non-HIV infections, hypergammaglobulinemic states, connective tissue disorders, or pregnancy (alloantibodies). Specimens with this result type are automatically tested for HIV-1 antibodies by Western blot assay (HV1WB / HIV-1 Antibody Confirmation by Western Blot, Serum) for further resolution. See interpretation and recommendations on results generated by HIV-1 antibody confirmation by Western blot.
Simultaneously reactive HIV-1 and HIV-2 results may be due to one of the following causes: a) HIV-1 infection with false-positive HIV-2 antibody results; b) HIV-2 infection with false-positive HIV-1 antibody results; c) dual infection with HIV-1 and HIV-2; d) false-positive results for both HIV-1 and HIV-2 antibodies. Specimens with this result type are automatically tested for both HIV-1 antibodies by Western blot assay (HV1WB / HIV-1 Antibody Confirmation by Western Blot, Serum) and HIV-2 antibodies by line immunoassay (HIV2L / HIV-2 Antibody Confirmation, Serum).
Reactive HIV-2 antibody but negative HIV-1 antibody results suggest the presence of HIV-2 infection. To rule out possible false-reactive HIV-2 antibody results, specimens with such results are automatically tested for HIV-2 antibodies by line immunoassay (HIV2L / HIV-2 Antibody Confirmation, Serum).
Unreadable results for both HIV-1 and HIV-2 antibodies indicates the persistent presence of smear or discoloration that interferes with proper reading of the test spots, suggesting nonspecific binding of antibodies in the patient's serum to the test membrane. Specimens with this result type are automatically tested for both HIV-1 antibodies by Western blot assay (HV1WB / HIV-1 Antibody Confirmation by Western Blot, Serum) and HIV-2 antibodies by line immunoassay (HIV2L / HIV-2 Antibody Confirmation, Serum).
The following testing algorithm is available in Special Instructions:
-HIV Testing Algorithm (Fourth Generation Screening Assay) Including Follow-up of Reactive HIV Rapid Serologic Test Results
Cautions Discusses conditions that may cause diagnostic confusion, including improper specimen collection and handling, inappropriate test selection, and interfering substances
This test is not offered as a screening test for HIV infection in symptomatic or asymptomatic individuals. It is not to be used as a screening or confirmatory test for blood donor specimens.
This test is not offered for maternal/newborn HIV screening for specimens originating in New York State.
Negative results for both HIV-1 and HIV-2 antibodies do not rule out acute HIV infection. If acute HIV-1 infection is suspected, detection of HIV-1 RNA (HIVQU / HIV-1 RNA Quantification, Plasma) or HIV proviral DNA (PHIV / HIV-1 Proviral DNA Qualitative Detection by PCR, Blood) is recommended. For patients at risk for HIV-2 infection (eg, having lived in West Africa or have sexual partners from West Africa), testing for HIV-2 DNA / RNA (FHV2Q / HIV-2 DNA/RNA Qualitative Real-Time PCR) is recommended.
All initially positive supplemental or confirmatory HIV test results should be verified by submitting a second specimen for repeat testing. Such positive HIV test results are required under laws in many states in the United States to be reported to the departments of health of the respective states where the patients reside.
Screening, supplemental or confirmatory serologic tests for HIV-1 or HIV-2 antibodies cannot distinguish between active neonatal HIV infection and passive transfer of maternal HIV antibodies in infants during the postnatal period (up to 18 months). Diagnosis of HIV infection in newborns and infants up to 18 months should be made by virologic tests, such as detection of HIV RNA (HIVQU / HIV-1 RNA Quantification, Plasma) or HIV proviral DNA (PHIV / HIV-1 Proviral DNA Qualitative Detection by PCR, Blood).
Participation in the recipients of HIV-1 vaccine (eg, participants in HIV-1 vaccine study trials) may develop vaccine-specific antibodies that may cross-react with this test and yield to the vaccine giving a positive, indeterminate, or unreadable HIV-1 antibody result while they may or may not be infected with HIV-1.
Assay performance characteristics have not been established for the following specimen characteristics:
-Presence of particulate matter
Reference Values Describes reference intervals and additional information for interpretation of test results. May include intervals based on age and sex when appropriate. Intervals are Mayo-derived, unless otherwise designated. If an interpretive report is provided, the reference value field will state this.
See HIV Serologic Interpretive Guide in Special Instructions for further interpretive information.
Clinical References Provides recommendations for further in-depth reading of a clinical nature
1. Bennett B, Branson B, Delaney K, et al: HIV testing algorithms: a status report. Association of Public Health Laboratories, April 2009. Available at http://www.aphl.org/aphlprograms/infectious/hiv/Documents/ID_2009April_HIV-Testing-Algorithms-Status-Report.pdf
2. Torian LV, Forgione LA, Punsalang AE, et al: Comparison of Multispot EIA with Western blot for confirmatory serodiagnosis of HIV. J Clin Virol 2011;52(Suppl 1):S41-S44
3. Wesolowski LG, Delaney KP, Hart C, et al: Performance of an alternative laboratory-based algorithm for diagnosis of HIV infection utilizing a third generation immunoassay, a rapid HIV-1/HIV-2 differentiation test and a DNA or RNA-based nucleic acid amplification test in persons with established HIV-1 infection and blood donors. J Clin Virol 2011;52(Suppl 1):S45-S49