A person infected with HIV produces antibodies specific to the virus as part of the body's immune response to the invader. Even though the antibodies are not enough to successfully fight HIV, they are of diagnostic value, as they can indicate the presence of the virus.

Antibody-based HIV testing is done, rather than a direct test for the virus itself, because it is too difficult to isolate the virus from the blood. Testing serves to determine if there is a viral infection in donated blood, tissues, or organs. This protects the recipients of the donated material and can be used to identify HIV-infected donors.

An antibody-based test cannot detect all HIV-positive blood. It can typically take between four and twelve weeks following HIV infection for antibodies to appear, although in rare cases this period can be up to one year. This interval between acquisition of the virus and the appearance of antibodies is called the window period. The introduction of tests that detect the viral nucleic acid rather than the HIV antibodies has markedly increased the detection sensitivity of blood screening. Still, even nucleic acid detection has a window period, albeit a shorter one, of about twelve days.

The fact that detection is not absolute from the moment of HIV infection means that the possibility exists that some HIV-infected donors may not be diagnosed and their blood may enter the nation's blood supply. However, the number of predicted contaminated blood samples is extremely small. To try to further reduce the chances of contaminated blood entering the blood supply, blood banks routinely question potential donors about high-risk behaviors. Any donor whose behavior might indicate an increased risk of HIV infection (such as intravenous drug use or unsafe sex) is automatically excluded from donating blood.

Two tests commonly used to detect HIV antibodies are believed to be about 99% reliable. These tests are the enzyme-linked immunosorbent assay (ELISA) and the Western blot.

Introduced in 1985, ELISA is a test designed for screening rather than diagnosing. The assay uses purified HIV antigens to probe for the presence of complimentary antibodies in a sample such as blood. If anti-HIV antibodies are present in the sample, they attach themselves to the viral proteins that have been immobilized on a plastic surface. A second antibody that has been raised against the anti-HIV antibody (antibodies are proteins too, and so can themselves function as antigens, stimulating the formation of antibodies) is bound to the anti-HIV antibodies. The second antibody also contains a chemical that can be made to change color. The color change reveals the presence of the anti-HIV antibody. If no color change appears, no anti-HIV antibody is present in the blood sample. This test is reliable, simple to conduct, and inexpensive.

The Western blot, introduced in 1987, is a confirmatory test. This means the test is commonly used to verify the results of the less-specific assays. The Western blot technique separates the various HIV proteins from one another, based on their speed of movement through a gel under the influence of electricity. The separated proteins are transferred from the gel to a membrane made of a material such as nitrocellulose. When the nitrocellulose is exposed to a blood sample, antibodies that recognize one of the proteins on the nitrocellulose will bind to the particular protein. As with ELISA, a color reaction can be induced to indicate the site of the bound antibodies. The Western blot provides a positive, negative, or intermediate result. The presence of three or more of the color bands confirms an HIV infection. If fewer--one or two--bands appear, the test is considered intermediate and retesting is performed six months later. If no color bands appear, the test is considered negative with no HIV present, though many people who test negative also repeat the test six months later.

In June 1998 the FDA approved a new, urine-based diagnostic kit for HIV marketed by Calypte Biomedical Corporation that does not require confirmation by a blood test. Urine tests are easier to use and cost less than blood tests for health-care providers. According to the National Institutes of Health, there is no evidence that HIV is spread through urine. Therefore, the chances of accidental infection through needle sticks or handling of samples are lessened. The urine test and its urine-based confirmation test, like most blood tests, recognize the existence of antibodies, not the actual virus.

The test is marketed to life insurance companies, clinical laboratories, public health agencies, the military, immigration authorities, and the criminal justice system. In the press release ''Calypte Appoints Distributor for Its HIV-1 Urine Test in People's Republic of China'' (June 12, 2000), Calypte announces its partnership with the Chinese National Center for AIDS Prevention and Control (NCAIDS) to distribute the first HIV-1 antibody urine test in the People's Republic of China. The NCAIDS estimated in 2000 that the total number of HIV infections in China could rise to as high as ten million before 2010 if proper countermeasures are not taken.

In July 2005 Calypte began marketing its products in developing countries; however, as of October 2007 Calypte rapid test products, which detect HIV-1 and HIV-2 antibodies in the blood, oral fluids, and urine, were not available in the United States. Calpypte (August 1, 2007) has distributors for its products in Africa, Asia, Brazil, Mexico, and the Middle East.

Thomas L. Schwenk indicates in ''Home HIV Testing Proves Accurate'' (Journal Watch Dermatology, April 1, 1997) that a recently approved home HIV test was analyzed in a 1997 multisite test study involving 1,255 people. Test participants registered anonymously by telephone with a testing laboratory. The subjects simply stuck a finger to draw blood and mailed the dried blood sample on filter paper to the laboratory. There, a phlebotomist (a health worker who draws blood by syringe or needle) matched the results with blood that had been drawn earlier from the patient's vein in the traditional manner. Results of the test were obtained by calling a toll-free telephone number. Negative results were given by recorded message. For positive results, a trained counselor offered callers follow-up information and counseling. Of the 1,255 people who participated, 1,104 participants called in to check their test results. For those participants the home test matched the phlebotomy results exactly.

Even though there is no new technology involved in home testing, it offers the advantages of privacy and ease of use. Critics of home testing point out that it is expensive; a kit costs as much as $65 and may be prohibitively expensive for poorer populations--for whom such a test is most needed. Critics also question the impersonal practice of relaying HIV-positive results and follow-up counseling by telephone.

As of 2007 the FDA had approved only the Home Access Express HIV-1 Test System, which is produced by the Home Access Health Corporation. The FDA warned that the more than one dozen non-approved home HIV tests advertised could produce inaccurate results. Home Access Health Corporation notes in the fact sheet ''What Is the Role of HIV Testing at Home?'' (August 1998) that in its first year it sold over 152,000 test kits and that 0.9% of people tested were positive for HIV.

During the mid- to late 1990s the CDC recommended the development of a new HIV test that would give results instantly. The CDC hoped that this would encourage people to learn the results of their tests. Currently, nearly seven hundred thousand people each year do not follow up to learn their test results. The CDC stresses the importance of obtaining results quickly. It contends that people are not only more likely to take a test that gives results instantly but also will benefit from the opportunity to learn they are infected before their immune systems have been seriously damaged. Furthermore, rapid results may lead to earlier, more effective treatment and might reduce transmission of the virus.

The FDA has approved a number of rapid-response tests designed for use in clinics in the United States. The first test to be approved is manufactured by Murex Diagnostics Inc. This test detects the presence of HIV antibody in about ten minutes. The test is as accurate as the standard Western blot test. However, because the Western blot test also looks for protein bands, this test remains the absolute antibody-based indicator of HIV.

In late 2002 the FDA announced approval of another blood-based antibody test (OraQuick Rapid HIV-1 by OraSure Technologies Inc.) for use. As of 2007 the test, which produces results within about ten minutes, was not licensed for home use and could only be performed in a clinical setting. However, the fact that the test does not require any specialized equipment or refrigeration offers the possibility of home use in the future.

Another similar rapid test kit, developed and manufactured by the Canadian-based MedMira Inc., was granted FDA approval in April 2003 for sale in the United States. The kit is also approved in China, where HIV infection rates dramatically increased in the early 2000s.

Rapid HIV tests are used more frequently in other countries, such as China. In developing countries, for example, quick-response tests are used to screen blood before transfusions and to screen pregnant women so medical interventions can be given to prevent mother-to-child transmission of the virus. They are also used in rural clinics.

In 2006 the CDC published ''Revised Recommendations for HIV Testing of Adults, Adolescents, and Pregnant Women in Health-Care Settings'' (Morbidity and Mortality Weekly Report, vol. 55, RR14, September 22, 2006). The new recommendations updated and replaced guidelines issued in 1993. The major revisions from the 1993 guidelines are to advise routine HIV screening of adults, adolescents, and pregnant women in health-care settings in the United States; to screen people at high risk for HIV infection at least annually; to eliminate the requirement for separate written consent for HIV testing, making general consent sufficient to permit HIV testing; and to remove the requirement to provide prevention counseling as part of HIV screening and testing programs in health-care settings. The 2006 guidelines also advise that HIV screening be part of routine prenatal screening for all pregnant women and that repeat screening during the third trimester of pregnancy be performed in areas where there are high levels of HIV infection among pregnant women.

In June 1996 the FDA approved a test to help determine how fast an HIV infection progressed to full-blown AIDS. Developed by Roche Diagnostic Systems Inc., the Amplicor HIV-1 monitor test is not intended to screen for HIV or to confirm an HIV diagnosis. Instead, the test detects the amount of HIV in the blood (the viral load) by measuring HIV genetic material. An increased viral load indicates the advancement of the infection toward AIDS and an increasing predisposition to the development of OIs. The test is based on a technique developed in 1984 called the polymerase chain reaction (PCR). PCR uses a heat-resistant bacterial enzyme to amplify the copies of target stretches of genetic material to detectable amounts. The process can be completed in less than one hour. This test was the first PCR-based test to be approved.

FDA approval was granted in 1997 to expand the use of the test as an aid in managing HIV in patients undergoing antiretroviral therapy. In 1999 a more sensitive version of the test became available.

Free term papers are not written to satisfy your specific instructions. You can use our professional writing services to buy a custom written research paper, term paper, or essay on HIV/AIDS at affordable price. CustomTermPapers is the best solution for those who seek help in writing term papers, essays, and research papers related to HIV/AIDS and other relevant topics.