HIV testing is vital for individuals to receive early treatment, care, and information to manage their disease. This includes information regarding the way to forestall passing HIV to people. The Centers for Disease Control and Prevention (CDC) suggests that everyone between the ages of 13 and 64 to get tested for HIV at least once as part of their medical routine. You may also need an HIV test if you are at higher risk of getting infected. HIV is mainly transmitted through sexual contact and blood, so you may be at an increased risk of contracting HIV if: ' You are a man who has had sex with another man ' You have had sex with an HIV infected partner ' You have had multiple sexual partners ' You injected yourself with drugs such as heroin or shared needles with another person
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In the United States, the Food and Drug Administration (FDA)-approved HIV serologic tests have historically been categorized as first-, second-, third-, and fourth-generation tests, based on evolving techniques and significant improvement in assay sensitivity.[ , ] With many of the new and improved HIV assays, a clear distinction between the HIV generations has blurred, and thus, use of the HIV test 'generation' nomenclature is no longer recommended.[ ] The first- and second-generation antibody assays are now referred to as IgG-sensitive tests, third-generation assays as IgM/IgG-sensitive tests, and fourth-generation as antigen-antibody immunoassays (Figure 6).[ , , , ] Further, the use of the term 'rapid HIV test' to describe point-of-care tests is no longer recommended, since a number of instrumented, laboratory-based tests now have the capacity to generate HIV test results in less than one hour. Instead, the type of test is considered either laboratory-based or point-of-care.[ , ]
The major tests used as screening tests for diagnosing HIV are (1) HIV antigen-antibody laboratory-based tests, (2) HIV antigen-antibody point-of-care tests, (3) HIV antibody laboratory-based tests, and (4) HIV antibody point-of-care tests.[ , ] There is also one FDA-approved HIV antibody test for use and interpretation at home.[ ] Further, HIV diagnostic testing includes HIV-1/2 differentiation assays and HIV nucleic acid tests (NATs). The NAT testing includes options for qualitative HIV RNA or proviral DNA PCR assays or a quantitative RNA PCR assay, which is commonly referred to as a viral load test. The following summarizes the major FDA-approved HIV screening and differentiation assays.[ , , ]
The HIV antigen-antibody laboratory-based immunoassays are the preferred screening tests for HIV. These immunoassays detect HIV-1 p24 (capsid) antigen and antibodies (IgM and IgG) to HIV-1 and HIV-2 (Figure 7).[ , , ] The HIV-1/2 antigen-antibody immunoassays detect HIV significantly earlier than laboratory-based antibody tests, point-of-care antigen-antibody tests, and point-of-care HIV antibody tests.[ , ] All reactive HIV-1/2 antigen-antibody tests require confirmatory testing. None of the HIV-1/2 antigen-antibody immunoassays can detect HIV-2 core antigen (p26 antigen), but cross-reactivity to HIV-1 p24 antigen can occur in persons with HIV-2.
The following list (in alphabetical order) summarizes the laboratory-based HIV-1/2 antigen-antibody immunoassays that are FDA-approved for use in the United States:[ ]
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This assay does not differentiate between p24 antigen and HIV antibodies. The ADVIA Centaur HIV Ag/Ab Combo Assay was evaluated in more than 7,000 samples and found to have a sensitivity of 98.4% and specificity of 99.7%.[ ]
This test is a chemiluminescent microparticle immunoassay (CMIA), and it requires less than 1 hour to perform.[ ]
This test does not distinguish antigen from antibody, nor does it distinguish HIV-1 from HIV-2. The ARCHITECT HIV Ag/Ab Combo assay has been evaluated in several studies and has demonstrated detection rates over 99% for established HIV infection and detection rates from 80% to 96% for acute HIV (with specificity above 98% in both established and acute HIV infection).[ , , ]
The ARCHITECT HIV Ag/Ab Combo is a CMIA, and it takes less than 30 minutes to perform.[ ]
An advantage of this test is it can differentiate between HIV-1 p24 antigen and antibodies to HIV-1 or HIV-2 and thus can help identify persons recently infected with HIV-1. Most other laboratory-based HIV antigen-antibody tests do not distinguish reactivity to p24 antigen from reactivity to HIV antibodies. Investigators prospectively tested the BioPlex HIV Ag-Ab Assay on 1,505 routine serum samples, and the assay had a sensitivity of 100% and specificity of 99.5%.[ ]
Additional testing on samples known to be positive for HIV-1, HIV-2, or both showed the differentiation capability of the assay was 100% for HIV-1, 90.7% for HIV-2, 100% for both HIV-1 and HIV-2, and 90.9% for early HIV infection.[ ]
This test is a multiplex flow immunoassay, and it takes 45 minutes to perform. A disadvantage of this test is it requires specialized equipment and specially trained technicians.[ ]
A reactive test does not distinguish p24 antigen from antibodies to HIV, and it does not distinguish HIV-1 from HIV-2. This test is an electrochemiluminescence immunoassay (ECLIA), and it takes 27 minutes to perform.[ ]
This assay evaluates serum or plasma samples for p24 antigen and antibodies to HIV-1 and HIV-2.[ ]
An advantage of this assay is that it differentiates p24 antigen reactivity from HIV-1 or HIV-2 antibody reactivity (the test gives an overall reactive or nonreactive result plus a sub-result that shows whether the p24 antigen or anti-HIV antibody,& or both, were positive). Although this test is one of a few antigen-antibody tests that distinguish between p24 antigen and anti-HIV antibody reactivity, it does not distinguish positive HIV-1 antibodies from positive HIV-2 antibodies.[ ]
This laboratory-based test can be completed in approximately 18 minutes.[ ]
A reactive test does not distinguish p24 antigen from antibodies to HIV, and does not distinguish HIV-1 from HIV-2. In a performance evaluation, the GS HIV Combo Ag/Ab EIA was shown to be 100% sensitive in detecting established, previously confirmed HIV and more than 85% sensitive in detecting acute HIV infection, with specificity above 99% in both groups.[ ]
This test uses an EIA microwell format, and it takes at least 3 hours to perform. This is one of the only FDA-approved, laboratory-based, antigen-antibody assays considered high complexity by CLIA. It is semi-automated (whereas the others are fully automated); it can be performed manually but is more labor-intensive and has a longer turnaround time as compared to other antigen-antibody assays performed in the laboratory.[ ]
Testing can be performed with serum or plasma samples. This test, however, does not distinguish between the reactivity of p24 antigen and HIV-1 or HIV-2 antibodies.[ ]
The laboratory-based test requires approximately 32 minutes.[ , ]
A reactive test does not distinguish p24 antigen from antibodies to HIV, and it does not distinguish HIV-1 from HIV-2. This assay is an immunometric 2-stage reaction, and it takes 48 minutes to perform.A CDC study evaluated the reactivity of HIV tests in specimens from individuals with HIV-1 seroconversion and showed that an HIV-1/2 antigen-antibody immunoassay was positive in 50% of persons at 17.8 days and in 99% at 44.3 days (Figure 8).[ ] Accordingly, the CDC considers laboratory-based HIV-1/2 antigen-antibody immunoassays to virtually exclude HIV infection if the test is negative 45 days after an exposure.[ ]
In the United States, there is only one FDA-approved point-of-care HIV-1/2 antigen-antibody test for the diagnosis of HIV:
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The Abbott Determine HIV-1/2 Ag/Ab Combo assay is the only FDA-approved point-of-care HIV-1/2 antigen-antibody test, and it is considered waived by CLIA when used for fingerstick whole blood. This assay can differentiate HIV-1 p24 antigen from HIV antibody, but it does not differentiate HIV-1 and HIV-2 antibodies.[ ]
The sensitivity of this assay for acute or very recent HIV infection is less than with laboratory-based HIV-1/2 antigen-antibody assays.[ , , ]
With this assay, the use of fingerstick whole blood specimens is not as sensitive as with plasma samples.[ ]
The Abbott Determine HIV-1/2 Ag/Ab Combo is a lateral flow immunochromatographic assay that takes 20 minutes to perform.The HIV enzyme immunoassay (EIA) antibody test for HIV diagnosis was first licensed in the United States in .[ ] For more than 20 years, HIV antibody tests were widely used as the initial laboratory diagnosis test in the HIV testing algorithm. Since , however, the use of HIV antibody tests as an initial screening test has been replaced by HIV antigen-antibody assays.[ , ] A reactive HIV antibody test always requires further confirmatory testing with another HIV assay.[ ] Most current laboratory-based HIV antibody tests are IgM/IgG-sensitive assays (as opposed to IgG-only assays) and can detect HIV IgM antibodies at approximately 23 to 25 days after HIV acquisition.[ ] The CDC considers these HIV antibody tests to have a window period of 90 days (even the IgM/IgG-sensitive assays); in this context, a negative HIV EIA test 90 days after a possible HIV exposure is considered to effectively rule out HIV acquisition from that exposure.[ ]
Single-use, point-of-care HIV test kits have self-contained testing reagents and materials and typically can yield a test result within 40 minutes.[ , , ] There are 7 FDA-approved, rapid, point-of-care tests that the CDC identifies as suitable for use in clinical and nonclinical settings.[ ] Six of these tests detect antibodies to HIV-1 and HIV-2, and one detects antibodies only to HIV-1. These antibody test results are either reactive or nonreactive. Hence, none of the currently used point-of-care antibody tests can differentiate HIV-1 from HIV-2. Multiple reports have shown problems with false-negative and false-positive test results with the oral fluid point-of-care test. Single-use, point-of-care rapid antibody tests are less sensitive than laboratory-based antigen-antibody tests for the detection of early HIV.[ , , , ] All positive point-of-care HIV test results are considered to be a presumptive positive test and require further supplemental testing for confirmation of HIV.[ ] Single-use, point-of-care testing is primarily used for testing (1) in emergency room encounters where follow-up might be problematic, (2) persons in labor who had no HIV testing performed during their pregnancy, (3) in an occupational exposure to HIV when immediate results may be needed, and (4) in other clinical settings where a low likelihood of follow-up for HIV test results is anticipated.[ , , ] The following list summarizes the current FDA-approved single-use, point-of-care, rapid HIV tests (in alphabetical order):[ ]
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This assay can be performed on samples of oral fluid, fingerstick whole blood, venous whole blood, serum, or plasma. This immunochromatographic test utilizes the Dual Path Platform (DPP) and requires 10-15 minutes to perform with blood samples and 25-40 minutes for oral fluid.[ ]
Tests can be performed using fingerstick whole blood, venous whole blood, serum, or plasma samples. This immunochromatographic lateral-flow test requires 15 minutes to perform.[ ]
This test is approved for use with fingerstick whole blood, venous whole blood, serum, or plasma samples. This immunochromatographic lateral-flow test requires 15 minutes to perform.[ ]
This test is approved for use with fingerstick whole blood, venipuncture whole blood, and plasma samples. This flow-through immunoassay requires only 2 minutes to perform.[ ]
This assay can be performed on samples of oral fluid, fingerstick whole blood, venous whole blood, or plasma. This lateral flow immunoassay requires 20-40 minutes to perform.[ ]
The following samples are FDA-approved for testing: fingerstick whole blood, venipuncture whole blood, serum, and plasma. This vertical flow immunoassay requires less than 3 minutes to perform.[ ]
This test is indicated for use with fingerstick whole blood, venous whole blood, serum, or plasma samples. This lateral-flow immunoassay requires 15-20 minutes to perform.Although several tests can distinguish HIV-1 from HIV-2, only one is currently in use (the Geenius HIV-1/2 Supplemental Assay), which is approved by the FDA as an HIV-1/HIV-2 differentiation assay.[ , ] Differentiating HIV-1 and HIV-2 is important to avoid misclassification of HIV infection; studies have shown that the HIV-1 Western blot was erroneously interpreted as positive for HIV-1 in 46% to 85% of specimens from persons with HIV-2.[ ]
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This assay utilizes multiple recombinant or synthetic peptides to detect HIV-1 antibodies (p31, gp160, p24, and gp41) and HIV-2 antibodies (gp36 and gp140). The test cassette contains 7 test lines, including the 6 HIV peptides and one control. A positive HIV-1 result requires at least 2 envelope peptides (gp160 and gp41) or 1 envelope peptide plus either the p24 or the polymerase peptide p31; a positive HIV-2 diagnosis requires reactivity to both HIV-2 envelope peptides gp36 and gp140.[ ]
Investigators have shown the Geenius HIV 1/2 Supplemental Assay is a reliable HIV confirmatory assay, and this test is recommended by the CDC as the differentiation assay to use in the HIV testing algorithm.[ , , , , ]
. The result may indicate reactivity for HIV-1, reactivity for HIV-2, or reactivity for both in cases of HIV-1/HIV-2 coinfection. It may be run on serum, plasma, or whole blood.The HIV-1 Western blot has been largely replaced by more sensitive and specific HIV diagnostic tests. When used, the HIV-1 Western blot can detect human antibodies that react to HIV-1 proteins that originate from three HIV-1 gene regions: env (gp41, gp120/160), pol (p31, p51, p66), and gag (p15, p17, p24, p55) (Figure 10).[ ] The HIV Western blot typically becomes positive after about 5 to 6 weeks following HIV acquisition; as more protein bands become detectable, the Western blot typically evolves from a pattern of negative, then indeterminate, then positive.[ ]
When HIV testing is performed by the person undergoing testing, it is referred to as self testing or in-home testing. With the OraQuick In-Home HIV Test, the testing is done in its entirety at home (or in another private location). With the Home Access HIV-1 Test System, the specimen is collected at home (or in another private location) and mailed in for testing. Both of these commercially available tests provide individuals with an option for anonymous HIV testing. Self-testing may be preferable for some people who are reluctant to undergo HIV testing in medical settings.[ , ] Studies have shown that self-testing is feasible and acceptable for persons undergoing testing,[ , , , , ] though several concerns persist, including (1) the cost of the test, (2) low sensitivity for detecting recent HIV acquisition, (3) lack of appropriate counseling and confirmatory testing for a positive test result, and (4) insufficient resources for linkage to care for persons with a positive test or linkage to HIV PrEP services for people with a negative test result.
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The test involves collecting an oral sample with a test device, placing the test device in a test kit vial that contains a developer solution, and then waiting 20 minutes to read the test result (the test must be read within 40 minutes). The client must read and interpret the test result. The test costs approximately $40, and it includes a full set of easy-to-follow instructions. As with all other rapid tests, a positive in-home HIV test result is considered a preliminary positive HIV test result and confirmatory HIV testing is required. This test is offered by some public health programs for screening in other non-clinic settings for individuals who may not access healthcare and clinic-based testing options.In the United States, HIV nucleic acid tests, including qualitative HIV RNA and quantitative HIV RNA assays, are used as part of the HIV diagnostic algorithm.[ ] Given the very low limit of detection of most HIV quantitative HIV RNA assays, many clinicians now use quantitative HIV RNA tests (also known as viral load tests), rather than the FDA-approved qualitative HIV RNA assays, for diagnostic purposes. The quantitative tests are more widely available than the qualitative tests, as they are routinely used in the clinical management of persons with established HIV.[ , ] For routine HIV screening, the HIV NAT tests are not typically used due to high cost, technical complexity, and the failure to detect HIV elite controllers (the approximately 0.5% of individuals with HIV who maintain undetectable HIV RNA levels without antiretroviral therapy).[ ] Instead, the HIV RNA tests are primarily used for confirmatory purposes. The HIV NAT is sometimes used for non-confirmatory purposes, including in persons being evaluated for acute HIV and persons receiving HIV PrEP (either oral or long-acting injectable HIV PrEP).[ ] In this setting, the HIV-1 NAT is often used in combination with HIV-1/2 antigen-antibody testing to (1) exclude HIV prior to initiating HIV PrEP and (2) to assist in the diagnosis of HIV in persons receiving HIV PrEP, since persons who acquire HIV while taking HIV PrEP can have negative or ambiguous HIV screening test results if HIV-1/2 antigen-antibody testing alone.[ ]
HIV nucleic acid testing may be used in four situations as an HIV diagnostic test:
In the United States, there is currently only one HIV RNA NAT that is FDA-approved for HIV diagnostic purposes:
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This assay can detect all major HIV-1 groups and subtypes and has a manufacturer reported detection rate of 98.5% for 30 copies/mL, 82.6% for 10 copies/mL, and 42.5% for 3 copies/mL.[ , ]
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The APTIMA HIV-1 RNA Qualitative Assay requires at least 3 hours to perform.