After a person becomes infected with HIV, the body's immune system recognizes the virus as a foreign intruder and begins to make antibodies to the virus. Antibodies against HIV usually take 1-3 months to develop, rarely longer. Tests to determine if a person is infected with HIV check for the presence of these antibodies. The current HIV antibody blood tests detect antibodies 99% of the time within 3 months of infection.
The benefits of testing for HIV include determining HIV status.If you are HIV-infected, the benefits of testing include:
- Ability to access HIV evaluation and care, including immune system monitoring and early drug treatments. This care is available to all people with HIV in WA state, even those without health insurance or financial resources (in King County, information for patients about individual health benefits can be accessed through the Lifelong AIDS Alliance) .
- Ability to reduce risk behaviors that expose sexual or needle sharing partners to HIV infection.
- Ability of a pregnant woman to receive antiviral drug treatment during pregnancy and delivery to greatly reduce the risk of transmitting HIV to her baby.
- Ability to inform (and to obtain Public Health help informing) current and previous sex and needle sharing partners of their risk of HIV infection.
- Decreased anxiety from finally knowing HIV status.
If you are not infected, the benefits of testing may include:
- Client-centered counseling that has been shown to reduce risks of future infections.
- Decreased anxiety from finally knowing HIV status.
- Ability to make decisions about condom use with a partner who has also been tested.
Disadvantages of testing for HIV include:
- Anxiety while waiting for test results. (Testing anxiety can be decreased through rapid HIV testing which provides results in 15-30 minutes.)
- The emotional and psychological consequences of dealing with a positive result.
- The potential for discrimination against those who test positive. However, in WA state it is illegal to discriminate based on HIV status. Anonymous testing and anonymous early clinical evaluation is available through Public Health to limit unwanted disclosure.
- The possible inability to get life or disability insurance if you are HIV positive. (Health insurance is available in WA state for all HIV positive individuals.)
Testing in most situations involves:
- Giving informed consent, which may require signing a form.
- Talking before testing with a test counselor about one’s sexual and drug using behaviors, the meaning of a positive or negative test result, and any other questions that may come up about HIV.
- Drawing a small amount of blood, or providing a saliva or urine sample.
- For regular antibody tests, results are given in about a week either by phone or in person. (Rapid test results are given more quickly.)
The most common and most accurate test to determine if someone is infected with HIV is the HIV antibody test. The test actually consists of two tests: a screening test and a confirmatory test. The screening test procedure is called an ELISA -- Enzyme Linked Immuno-Sorbent Assay or an EIA (Enzyme Immunosorbent Assay). The confirmatory test procedure used is either a Western Blot Assay (WB) or an Indirect Immunofluorescense Assay (IFA). The screening and confirmatory tests are usually done using small samples of blood. If a sample of blood tests positive repeatedly in the screening test, it will be confirmed through the Western Blot test. Except when rapid testing is done, test counselors inform people they are infected with HIV only after both the screening and confirmatory tests have shown a positive (reactive) result.
Positive HIV antibody tests results are over 99% accurate when confirmed. Negative HIV antibody tests are over 99% accurate if it has been at least three months after a contact with a potentially HIV-infected partner. False negatives or false positives occur rarely.
The time period between a person's actual infection with HIV and until HIV antibodies become detectable in blood or other fluids is called the "window period". Most people will develop antibodies detectable with the latest blood tests within 4-6 weeks after infection with HIV. Some people may take longer; but nearly all (99%) will have antibodies by 3 months following infection. Therefore, we recommend that people wait 3 months from the time of the possible infection with HIV (the date of latest exposure) before being tested for HIV antibodies. The test may not give an accurate negative result if a person gets tested too soon after a potential exposure.
People waiting three months from the time of the exposure before testing will have a 99% accurate test result. Very rarely, cases have been reported of people taking longer than three months to develop antibodies to HIV.
Home self-collection test for HIV
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The HIV home tests are really self-collection devices coupled with a distant lab and a phone results service. A person collects a small sample of his/her own blood through a finger prick and then sends the sample to a laboratory to be tested (using both the screening and confirmatory tests, if needed) for antibodies to HIV. Anonymity is maintained through an identification code number. Results are obtained over the phone by calling a toll-free number and entering the unique identification number. The Home Tests have the same accuracy and the same window period as the regular HIV antibody tests.
Home AccessTM is the only FDA approved self collection test. It can be purchased through drug stores or on the Internet. Some other home self-tests are illegally sold over the internet. At this time (May 2000), none of these have been approved by the FDA and some have very poor accuracy. Non-FDA approved tests should always be avoided.
The advantages of the home tests are anonymity and convenience. The privacy of the home tests offer some people more comfort than going to a public test site; no appointments are necessary, and other barriers to clinic testing such as transportation and child care are avoided.
The disadvantages of the home tests include: no in-person counseling, having to prick your finger to obtain a blood sample, possibly outdated referrals for further counseling or care, and the cost of the test kit ($30-$50). Face-to-face counseling may provide more effective emotional support, risk reduction to help avoid future infection, and better referrals to psychotherapy and medical treatment. Home tests may also reduce the ability of public and other health care professionals to help assure notification of partners of their potential infection and to track new HIV infections.
The p24 antigen test identifies actual HIV viral particles in blood (p24 is a protein specific for HIV). However, the p24 antigen test is generally only positive from about one week to 3 - 4 weeks after infection with HIV. The p24 protein cannot be detected until about a week after infection with HIV, because it generally takes that long for the virus to become established and multiply to sufficient numbers that they can be detected. The p24 antigens then become undetectable again after sufficient antibodies to HIV have been produced, because they bind to the P-24 protein and eliminate it from the blood. Once antibodies are produced, the p24 test will register negative even in people who are infected with HIV. Of course, at that point the regular HIV antibody test will then be positive.
The p24 antigen test has very limited value in diagnosing HIV infection. It has been used in HIV research and, since 1996, has been used as an additional screening test in blood banks to help reduce the window period and reduce the possibility of HIV infected blood being used in transfusions.
Most people will not benefit from having a p24 antigen test. People who have engaged in behaviors that may have put them at increased risk of infection with HIV should not give blood in order to be tested by the blood bank. Instead, call the HIV/STD Hotline at (206) 205-7837 for options to get HIV testing.
Viral load testing is the direct measurement of the amount of HIV present in the blood. Several different tests identify and measure the genetic material resulting from virus infection, either RNA or DNA. These tests are also called nucleic acid tests. The laboratory procedure used to test for the genetic material of HIV is called the Polymerase Chain Reaction (PCR) test. PCR viral load testing is usually done to allow doctors to track how active HIV is in a person’s body to help make antiviral treatment decisions. PCR tests are also used in research on primary HIV infection.
The FDA has not approved these PCR tests as ways to identify new HIV infections. The regular antibody test continues to be the most accurate and reliable way for people to know if they are infected with HIV. PCR tests may be negative in people with HIV if their infection is so recent (e.g, less than 5 days old) that virus has not yet begun to produce detectable quantities of virus, or if they have brought the infection under control spontaneously or with the help of the new potent anti-retroviral medications. Occasionally, PCR tests also can be falsely positive in the absence of HIV infection. The test is also very expensive (around $150) and cannot be done anonymously except through certain research studies. (In Seattle, see the Primary Infection Research Clinic.) Finally, any PCR test used to identify infection must be followed by a regular HIV antibody test taken three months after exposure to confirm the PCR test result. PCR viral load tests are most useful in people who already know their HIV status and to help make antiviral drug treatment decisions.
Viral load testing has become a standard method of monitoring viral activity and is used to monitor the success of antiviral treatment. Results from viral load tests can range from "undetectable" to over a million copies per milliliter of blood. Lower numbers mean fewer viruses in the blood and less active disease; higher numbers mean more viruses in the blood and more active disease. The goal of antiviral treatment is to substantially reduce the viral load. Viral load tests are used to determine when to start treatment and when to change or stop treatment. An "undetectable" viral load does not mean that the person is free of HIV infection. Most viral load tests can only detect down to the level of 40 viral particles per milliliter of blood. Thus "undetectable" means less virus per milliliter than this test can measure (e.g., up to 39 viral copies per milliliter.)
A person with an "undetectable" viral load is still infected with HIV and can still infect others. Viral loads measure the amount of virus in the blood; most transmission is sexual and sexual fluids may contain measurable virus even when blood virus is undetectable. Generally, however, the higher one's viral load the more likely one is to transmit the virus and the lower one's viral load the less likely one is to transmit the virus.
The "less sensitive" HIV antibody test
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A new test called the "detuned" or "less sensitive" ELISA is now being used in some testing and research sites to determine if a newly found HIV infection is likely to represent a recent HIV infection (acquired within the last 4-6 months). This information can help providers and patients make anti-retroviral treatment decisions, to help focus partner notification efforts, and to help people in public health better understand the spread of recently acquired HIV infection. The less sensitive test is used only after someone is shown to be infected with the virus by using the regular HIV antibody test.
People recently infected have lower overall levels of antibodies to HIV than those who have been infected for a longer periods of time. If a person has recently been infected with HIV (within the past 4-6 months), that person will test positive on the regular (very sensitive) HIV antibody tests but may test negative when the patient’s serum is diluted and the test is incubated for a shorter than normal period of time (the less sensitive test.) In contrast, a person infected more than 6-8 months previously will test positive on both the regular antibody test and the less sensitive test. The CDC is studying the performance of this new test and its potential use around the country to help better understand the spread of new HIV infections. (See also HIVIS--HIV Incidence Study in Seattle-King County.)
HIV tests using saliva (oral fluids) or urine
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Tests are now available and FDA approved for using oral fluids or urine to test for antibodies to HIV. (Note: oral fluids (including saliva) and urine contain antibodies to HIV—they do not contain HIV itself. HIV is NOT transmitted through oral fluids or urine.) Like a typical blood test for antibodies to HIV, the oral fluid and urine tests actually consist of two tests: a screening test and a confirmatory test. The screening test is also called an ELISA (Enzyme Linked Immuno-Sorbent Assay) or an EIA (Enzyme Immunosorbent Assay). The confirmatory test procedure used is either a Western Blot Assay (WB) or an Indirect Immunofluorescense Assay (IFA). Tests using oral fluids or urine samples have the same accuracy as the regular HIV antibody tests and the same window period limitations.
Studies have found that oral fluid tests are more acceptable to people at high risk, and some tests sites are beginning to offer the oral fluids test (called OraSure) as an alternative to regular blood testing for people with very poor veins or those with severe needle phobias. However, the higher cost of the oral fluids tests ($24) limits its routine use in most clinics.
The urine test for HIV is generally used in countries outside of the United States and by insurance companies. The urine test is not routinely available to consumers but can be ordered by a doctor. Because a doctor must order it, the urine test is not generally performed anonymously.
The FDA approved a rapid test for detecting HIV antibodies in 1996. The technology used to perform this test is called the Single Use Diagnostic System (SUDS) for HIV. This system is a screening test using a small sample of blood, comparable to the ELISA/EIA. It is more than 99% accurate when used 3 months after possible exposure; however, positive results on a SUDS test need to be confirmed by the usual Western Blot or the Immunoflourescence Assay confirmation tests performed on blood. The results of the SUDS test for HIV are available after 15-30 minutes, but only negative results can be reported at that time. Positive results are provided tentatively, based on the prevalence of HIV infection in the subject’s risk group. For example, a gay man with a positive result living in a community in which 10-20% of gay men carry HIV, would be told that the result means that he is very likely infected with HIV, but that he should return in a week to obtain the results of the confirmatory test. Whereas a client from a population at lower risk would be told that they may have been infected with HIV, but it is just as likely that the result is a false positive.
Advantages
- The obvious advantage of rapid HIV testing is that people who are negative for HIV can get results right away.
- Research has shown that these tests are more acceptable to people at high-risk than the standard HIV test, because it eliminates the week of anxiety that people experience while waiting for results.
- People involved in high risk behavior can also learn that they are probably HIV-infected when their SUDS is positive. They are more likely to come back to receive their final test results and get help with partner notification, than those who test with the standard method.
- In certain situations such as occupational exposure, rape or prenatal care and delivery, rapid identification of HIV infection can result in timely initiation of antiviral treatment, which may prevent HIV infection. (See Post Exposure Prophylaxis for further information)
Disadvantages
- Positive results from the rapid HIV test need to be confirmed by another test, which takes up to one week.
- There can be a fairly high level of false positives when the rapid tests are used in lower-risk populations. The level of anxiety in those initially testing positive by the rapid test may be higher than those awaiting results of the regular test..
- The rapid tests also cost more than the regular antibody test. However, since so many more people receive test results with rapid testing, it has been shown to be cost-effective in high-risk populations.
Rapid testing is currently being used in publicly funded out-reach testing, and its use will likely continue to expand as less expensive and more simple rapid tests become available (several are currently going through clinical trials).
Confidential vs. anonymous testing
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Confidential Testing means that the clinic keeps the patient name in their records and must keep the medical record information (like all other recorded information) private; they are generally prohibited from releasing HIV information except by written permission. (Patients often sign a "consent to bill" form, which gives permission to release information to an insurance company. Patients can check this with their provider.)
Anonymous Testing means that the clinic keeps no record of the patient name; they use only a code to process records and blood specimens.
(See also Pros & cons of "anonymous" and "confidential" HIV testing)
HIV & AIDS surveillance in Washington State
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Named surveillance (also known as named reporting) for AIDS has been in place since 1984. In mid-1999 the Washington State Board of Health voted to implement HIV case reporting starting September 1st, 1999. Both adult/adolescent and pediatric HIV cases are reported by providers and labs. The HIV reporting plan as adopted in Washington is unique among all the 50+ reportable diseases in that names are used for asymptomatic HIV infection only to assure the completeness of case reports and within 3 months after the case report is complete, all identifiers are converted to a non-name code. For more information see the HIV/AIDS Epidemiology Fact Sheet or call 206-296-4645.
The availability of anonymous testing is considered a vital part of testing options in King County and Washington State. Positive results obtained through anonymous testing are not reportable. However, when HIV positive patients are seen for health care, or tests are obtained, the health care provider and labs must report the case. Public Health-Seattle & King County does, however, offer an initial anonymous clinic visit with a complete exam and viral load testing, so that people can make informed decisions about seeking health care. Anonymous testing is available through local health departments and other community organizations and through home testing kits. Sites offering anonymous testing can be located by calling the HIV/STD Hotline at 206-205-7837.
Testing for other types of HIV
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There are two types of HIV (HIV-1 and HIV-2). Both HIV-1 and HIV-2 have been identified in the United States, but HIV-2 infection is quite rare--approximately 100 cases total. HIV-1 is divided into two groups: Group M (major) and Group O (outlier). Group M is then divided into subtypes A through I. In the United States, the predominate HIV-1 subtype is B.
Some people have concerns that HIV antibody tests will not correctly identify infection with an uncommon type or variety of HIV. Studies by the CDC show that infection with unusual types or strains of HIV in the United States is rare. In addition, the regular antibody tests will pick up most of the unusual types or strains. In certain situations in which there is a high suspicion of an unusual HIV infection, specimens can be sent to the CDC for special analysis.
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