Serological tests for HIV

BACKGROUND

The human immunodeficiency virus (HIV) is a retrovirus that causes AIDS (acquired immune deficiency syndrome). The retrovirus primarily attacks the immune defense system, making the patient extremely vulnerable to opportunistic infections.

HIV is transmitted from person to person via bodily fluids including blood, semen, vaginal secretions, and breast milk. Therefore, it can be spread by sexual contact with an infected person, by sharing needles/syringes with someone who is infected, through breastfeeding, during vaginal birth or, less commonly (and rare in countries where blood is screened for HIV antibodies), through transfusions with infected blood. HIV has been found in saliva and tears in very low quantities and concentrations in some AIDS patients. However, contact with saliva, tears, or sweat has never shown to result in HIV transmission.

Currently, there is no cure for HIV/AIDS. Patients receive antiretroviral drugs, which suppress the virus. These drugs do not reduce the risk of transmitting the disease to someone else.

HIV can infect and kill many different types of cells in the body, but the primary targets are immune cells called CD4 T-cells. The CD4 T-cells are a type of T-lymphocyte (white blood cells) that helps coordinate the immune system's response to infection and disease.

The first stage of HIV, known as the primary or acute infection, is the most infectious stage of the disease, and it typically lasts several weeks. During this phase, the virus replicates rapidly, which leads to an abundance of the virus in the bloodstream, and a drastic decline in the number of CD4 T-cells. The CD8 T-cells (cells that kill abnormal or infected body cells) are then activated to destroy HIV-infected body cells and antibodies are produced. An estimated 80-90% of HIV patients experience flu-like symptoms during this stage.

The next stage, called clinical latency, may last anywhere from two weeks to 20 years. During this phase, HIV is active in the lymph nodes, where large amounts of the virus become trapped. The surrounding tissues, which contain high levels of CD4 T-cells, may also become infected. The virus accumulates in infected cells and in the blood as free virus.

Patients progress to AIDS when their CD4 cell counts drop below 200 cells per microliter of blood. Healthy individuals have a CD4 cell count between 600 and 1,200 cells per microliter of blood. Individuals with a CD4 cell lower than 200 cells per microliter of blood have the greatest risk of developing opportunistic infections.

The U.S. Centers for Disease Control and Prevention (CDC) estimates that about 1-1.2 million Americans were living with HIV at the end of 2003. About 25% of these HIV-positive individuals (252,000-312,000) were unaware of their HIV-status, and therefore, likely to have unknowingly transmitted the infection to others.

Patients who are diagnosed with HIV in the early stages of infection have better survival rates because they have early access to antiretroviral drugs. Regular testing may also decrease the number of new diagnoses. Several cohort studies have shown that many HIV patients reduce risky behaviors that can potentially transmit the virus after they find out that they have HIV.

NEW HIV TESTING GUIDELINES

The U.S. Centers for Disease Control and Prevention (CDC) recently updated their HIV testing guidelines in 2006. The CDC recommends that all individuals ages 13-64 be tested for HIV annually. The CDC also emphasizes that all HIV tests should be voluntary, and no tests can be performed without the patient's consent. In addition, the new guidelines no longer require pre-test counseling. While pre-test counseling must still be offered to all patients, it is now an option, not a requirement for the patient to participate. Also, written consent forms are no longer mandated. Instead, oral consent is sufficient.

If the HIV status of a pregnant woman is unknown when she gives birth, the CDC recommends that women be voluntarily screened for HIV with a rapid HIV test immediately after delivery. In addition, rapid HIV testing is recommended for newborns when the mother's serostatus remains unknown. The CDC also recommends repeat HIV testing during the third-trimester of pregnancy in women who live in areas with high HIV prevalence.

WHO SHOULD GET TESTED

The U.S. Centers for Disease Control (CDC) recommends that the following individuals get tested for HIV:

Individuals between the ages of 13 and 64 should be tested annually.

Individuals who have injected drugs or steroids and shared equipment with others.

Individuals who have had unprotected vaginal, anal, or oral sex.

Individuals who have multiple or anonymous sexual partners.

Individuals who have exchanged sex for drugs or money.

Individuals who been diagnosed with or treated for hepatitis, tuberculosis (TB), or a sexually transmitted disease (STD), like syphilis, gonorrhea, or chlamydia.

Individuals who have come in direct contact with an HIV-infected person's blood.

Individuals who had unprotected sex with someone who could answer "yes" to any of the above questions.

Pregnant women should be screened for HIV as part of regular prenatal tests.

TYPES OF TESTS

As soon as the virus enters the body, the immune system produces antibodies, which are proteins that detect foreign substances like viruses that enter the body. The presence of these antibodies in the blood, oral fluid, and urine can be used to determine whether HIV is in the body.

It may take some time for the immune system to produce enough antibodies for the antibody test to detect them. This time period, known as the "window period," varies among patients. Most people will develop detectable antibodies two to eight weeks after exposure, with the average being 25 days. However, some individuals might take longer to develop detectable antibodies. Ninety-seven percent of people develop antibodies in the first three months following the time of their infection. In very rare cases, it can take up to six months to develop antibodies to HIV. Therefore, if the initial negative HIV test was conducted within the first three months after possible exposure, repeat testing should be considered longer than three months after the exposure.

The test results must remain confidential. Individuals who are younger than 18 years old can consent to or refuse to be tested for HIV, without the involvement of their legal guardians. Test results may not be released to the patient's legal guardian(s) without his/her consent.

Enzymelinked immunosorbent assay (ELISA): The most common HIV tests use blood to detect HIV infection. In most cases the enzyme-linked immunosorbent assay (ELISA) tests a patient's blood sample for antibodies. Oral fluid (not saliva), collected from the cheeks and gums, may also be used to perform an ELISA. Oral fluid ELISA tests are considered as sensitive as a blood test. A urine sample may also be used during an ELISA, but this is considered less accurate than a blood or oral fluid test. A positive (reactive) ELISA for all samples must be used with a follow-up (confirmatory) test, such as the Western blot test, to make a positive diagnosis Although false negative or false positive results are extremely rare, it may occur if the patient has not yet developed antibodies to HIV or if a mistake was made at the laboratory. When used in combination with a Western blot test, ELISA tests are 99.9% accurate.

Western blot test: A Western blot test is typically used to confirm a positive HIV diagnosis. During the test, a small sample of blood is taken and it is used to detect HIV antibodies, not the HIV virus itself. The Western blot test detects specific protein bands that are present in HIV patients. When used in combination with an ELISA, the Western blot test is 99.9% accurate.

Polymerase chain reaction (PCR): Polymerase chain reaction (PCR) tests are used to detect HIV's RNA (genetic material). These tests can be used to screen the donated blood supply and to detect very early infections before antibodies have been developed. This test may be performed just days or weeks after exposure to HIV. Although these tests are the most accurate, they are not performed as often as the other HIV tests because they are expensive and require the skill of a qualified scientist.

Rapid test: A rapid test produces results in about 20 minutes. Rapid tests use a sample of blood or oral fluid to detect HIV antibodies. The patient's sample is placed on a test strip that contains HIV antigens. If the patient has developed HIV antibodies, the strip changes colors, indicating a seropositive result. A positive HIV test should be confirmed with a follow-up confirmatory test before a final diagnosis of infection can be made. These tests have similar accuracy rates as traditional ELISA screening tests.

Home testing kit: Consumer-controlled test kits (popularly known as "home testing kits") were first licensed in 1997. The Home Access HIV-1 Test System™ is the only home kit that is approved by the U.S. Food and Drug Administration (FDA). The Home Access HIV-1 Test System™ is available at most local pharmacies. It is not a true home test, but rather a home collection kit. The individual pricks a finger with a special device and places drops of blood on a specially treated card. The card is then mailed to a licensed laboratory for testing. Home testing kits are confidential, and patients do not need to provide personal information, including their name and address, when submitting their samples. Instead, they have a personal identification number that is used to call for results. Callers may speak to a counselor before taking the test, while waiting for the test result, and/or after the results are given. All individuals who receive a positive test result are given referrals for a follow-up confirmatory test, as well as information and resources on treatment and support services.

HIV COUNSELING

Pre-test counseling: According to the U.S. Centers for Disease Control and Prevention's (CDC) new guidelines on HIV testing, HIV prevention counseling is not required to accompany HIV screening. However, the CDC still recommends that patients receive information about HIV testing, including the benefits, consequences, and costs. Patients must also receive information about the infection, including how it is transmitted, how it can be prevented, and where to obtain more information and services (like treatment). Healthcare providers should also tell patients when to expect results, what they mean, and that confirmatory testing is needed if the results are positive.

Information can be provided to the patient in a face-to-face meeting with a counselor or in a pamphlet, brochure, or video. Patients who are tested with a rapid HIV test should have equal access to the same types of information.

Prevention counseling: Prevention counseling is not mandatory, but it should be offered to all patients when they receive their test results.

Counseling should focus on reducing the risk of acquiring HIV infection or transmitting the infection. The counselor should make a personalized detailed risk assessment of the patient. The counselor should also suggest achievable behavioral changes that may reduce the patient's risk of developing HIV. The counseling session is a chance to clear up any misconceptions or questions that the patient has about the disease.

AUTHOR INFORMATION

This information has been edited and peer-reviewed by contributors to the Natural Standard Research Collaboration (www.naturalstandard.com).

• AIDS.org. www.aids.org. Accessed April 11, 2007.
• Centers for Disease Control and Prevention. www.cdc.gov.Accessed April 11, 2007.
• HIV InSite. http://hivinsite.ucsf.edu. Accessed April 11, 2007.
• Natural Standard: The Authority on Integrative Medicine. www.naturalstandard.com. Copyright © 2007. Accessed April 11, 2007.
• The Body: The Complete HIV/AIDS Resource. www.thebody.com. Accessed April 11, 2007.