Saturday, January 30, 2010

HIV 101 - HIV test

What is an HIV test?

An HIV test shows if someone is infected with HIV, the virus that attacks the body's immune system and causes acquired immune deficiency syndrome, or what is more commonly known as AIDS. There are several different tests that can be used to determine if you are carrying the HIV virus. The first test developed is still the most frequently used for the initial detection of HIV infection: the enzyme-linked immunosorbent assay or as it's more commonly known, the ELISA or EIA.

The ELISA is usually done by drawing blood, usually from a vein in the arm. The process is no more uncomfortable than a typical blood test. For most people, it is not particularly painful and the blood draw is accomplished quickly.

If the ELISA test is negative—meaning that antibodies are not found—the testing is complete. If the ELISA test is positive, the laboratory will want to make sure that it is not a "false positive" result (some molecules in the bloodstream can sometimes cause a false-positive result). First, they may repeat the ELISA test. If it's positive, they will conduct a test called a Western blot. If both the ELISA and the Western blot test yield a positive result, a diagnosis of HIV infection is confirmed and the results are sent back to the healthcare professional who ordered the test.

If you have blood drawn for an HIV test, it can take between one and two weeks to learn the results. If it seems as if you are waiting a long time to learn the results, this in no way means that the result is "positive" and that the laboratory needs more time to conduct additional tests.

When should you get tested and is the test result accurate?

There is a "window period" which is the time it takes the body to produce antibodies after HIV infection has begun. For the vast majority of those who will test positive, antibodies to HIV will develop within 4-6 weeks after exposure. Some will take a little longer to develop antibodies. To make certain that you receive a reliable test result, it's necessary to wait at least three months (13 weeks) after your last possible exposure to the virus before being tested.

Getting tested before three months may result in an unclear result or a false negative. Some testing centers may recommend testing again at six months. More than 99 percent of those who are going to seroconvert will do so within three months (seroconversion is the development of detectable antibodies to HIV in the blood as a result of infection.) It's extremely rare for seroconversion to take more than six months to develop detectable antibodies.

No diagnostic test will ever be 100 percent reliable, but if you test negative at the appropriate time (i.e., 13 weeks after possible exposure to the virus), you can consider that to be a dependable confirmation that you are HIV negative.

What are some of the other tests available?

These are other reliable, government-approved tests which are widely available:

Rapid Testing:

Samples are obtained and analyzed using the ELISA test. The results are usually available within ten to sixty minutes. If the result is positive, a follow-up test is required, usually by drawing blood and sending the sample to a laboratory for Western blot testing. If the result is negative, there is no need for additional testing and the result can be considered conclusive.

Convenient and faster, this method is often used in healthcare settings, particularly where urgency is an issue such as with someone who is pregnant or about to give birth. Because it provides a result so quickly, this is an increasingly popular method for testing.

Several rapid HIV tests have been approved for the FDA, all of which can only be performed by healthcare providers (they cannot be purchased directly by consumers). The approved tests are the Oraquick Rapid HIV Antibody Test (using oral fluid or blood samples), the Oraquick Rapid HIV-1/2 Antibody Test (tests for both HIV-1 and HIV-2 using blood samples), the Clearview Complete HIV 1/2 and HIV 1/2 STAT-PAK (a blood sample is used to check for antibodies to HIV-1 and HIV-2), the Reveal Rapid HIV-1 Antibody Test (requires a blood sample), and the Uni-Gold Recombigen HIV Test (requires a blood sample). While the time to conduct each of these tests do vary, they all yield results in less than an hour. If you are interested in any of these tests, you should call your healthcare provider to see if he or she conducts these tests and, if not, where you may go to have one done.

The collection of oral fluids to look for HIV antibodies using the Oraquick Rapid HIV Antibody Test may not be as accurate as the other rapid assays that use blood samples. There were reports starting in 2005 that some testing sites in Los Angeles, San Francisco, and New York City had higher rates of false-positive test results than usual, meaning that the Oraquick Rapid HIV Antibody Test using oral fluids (but not blood samples) falsely detected antibodies in people who were not infected with HIV. Most—though not all—of these sites later found that there were problems with how the tests were being handled by providers. However, the test is still highly accurate in terms of detecting antibodies in people who are infected with HIV (it has an extremely low false-negative rate).

It's very important to understand these new tests do not change the length of time you have to wait after a possible exposure to HIV to get a reliable result. You still need to wait three months (13 weeks), to allow time for antibodies to become detectable in the blood for an accurate result.

The Oraquick, Clearview, Reveal Rapid, and Uni-Gold Recombigen tests are not the only rapid tests available. Some hospitals, clinics and a few private doctors' offices have their own in-house rapid tests, which are also completely reliable.

Home Sample Collection Tests:

Using a provided safety lancet, you will need to prick your fingertip and place drops of blood on the blood specimen card included in the test kit. You only need enough blood to fill a circle the size of a dime. The kit will contain a unique identifying number that you'll need to have handy to learn the results. The blood specimen card is then sent to a designated laboratory where it is tested using the ELISA/Western blot tests. The results are usually available within three to seven days and are accessed by calling a telephone number provided by the laboratory. The results, along with counseling, are provided by trained counselors over the telephone.

Oral Fluid Test:

A device is used to collect oral (mouth) fluid (i.e. saliva). Oral fluids can contain antibodies to HIV, which can be detected using the ELISA and Western blot tests. The Oraquick Rapid HIV Antibody Test, which has a high degree of accuracy and produces results in less than an hour, can be conducted using oral specimens. Oral specimens are usually collected using the OraSure HIV-1 Oral Specimen Collection Device, which can then be tested using the rapid assay or traditional testing procedures. Because oral specimen collection is so easy and comfortable to accomplish, this test is often used in clinics, doctors' offices, hospitals, and school-based and university health centers.

Urine-Based Test:

A urine sample, collected in a cup, is used for the ELISA/Western blot tests. The results of this noninvasive and non-technical method can be obtained at a return visit, typically in one to two weeks. It's commonly used in community-based and outreach settings, adolescent, school and university-based settings. Anyone with a positive urine result must have a confirmatory blood test.

I can't wait 13 weeks to find out! Are there other options?

There are tests that can look for the virus—not antibodies—in the blood. Because the virus becomes detectable in the blood much sooner after infection than antibodies, these tests are an option for people who simply can't wait 13 weeks to find out the results of standard ELISA/Western blot testing. And because there has been some encouraging research indicating that people who diagnose their HIV infection early—meaning the first weeks after infection, before antibodies become detectable—can protect their immune systems by starting treatment early, these tests are proving to be very useful for people who recently engaged in a high-risk activity (e.g., receptive anal sex without a condom) and fear they might have been infected.

These tests look for fragments of HIV, either floating around freely in the bloodstream or inside cells in the bloodstream. Some tests—known as qualitative tests—yield a "positive" or "negative" result, meaning that the virus was or wasn't found (GenProbe's Aptima HIV-1 RNA Qualitative Assay is the only test approved for this purpose). Other tests—known as quantitative tests—yield a "viral load" result, meaning the amount of virus in a sample of blood. Roche's quantitative Amplicor HIV Monitor Test is frequently used by doctors and research centers but is not specifically approved for this purpose. It is only approved to monitor to people who are known to be infected with HIV, particularly to find out if their treatment is working properly.

These tests are highly sensitive, meaning that they can detect even the tiniest amounts of HIV in a blood sample. However, they are not always specific, meaning that they can sometimes yield a false-positive result. In turn, follow-up testing using standard ELISA/Western blot assays, is typically recommended.

These tests must be ordered by a health care provider, meaning that you should call your doctor if you think you may have recently been exposed to the virus and would like one of these tests. It's also important to keep in mind that these tests can be expensive and are not usually covered by insurance for diagnostic purposes.

Aren't there two different kinds of HIV? How do I know what I should be tested for?

The two known types of HIV are HIV-1 and HIV-2. In the United States and Europe, the overwhelming majority of HIV cases involve HIV-1. HIV-2 infections are predominantly found in West African nations. The first case of HIV-2 was discovered in the United States in 1987. Since then only 79 people with HIV-2 infections have been identified in the United States. While the CDC does not recommend routine screening for HIV-2, when someone tests for HIV-1 using ELISA/Western blot tests, there is a 60% to 90% chance that HIV-2 will be detected if it is present.

Not every test will automatically include testing for HIV-2. Anyone who thinks there's a possibility they have been exposed to HIV-2 and/or any of HIV's more rare subtypes should mention this when being tested. Among those for whom HIV-2 testing is indicated are those with sex partners from a country where HIV-2 is prevalent or people with an illness that indicate underlying HIV infection, such as an opportunistic infection, but whose HIV-1 test result was negative.

What about subtypes of HIV?

Thus far, 11 distinct subtypes, also known as "clades" or "genotypes," have been recognized of HIV-1. More than 96% of the HIV-1 infections in the United States and Europe are caused by subtype B. Subtypes B and F predominate in South America and Asia. Subtypes A through H of HIV-1 are found in Africa, along with HIV-2 in sub-Saharan Africa.

The ELISA/Western blot tests can detect antibodies to all HIV-1 subtypes. Viral load tests can also detect and quantify subtypes of HIV-1. The viral load tests can also detect and quantify HIV-2.

Should I get tested for HIV?

Getting tested is recommended if any of the following apply to you:

  1. You should be tested at least once a year if you are sexually active, particularly with three or more sexual partners in the last 12 months.

  1. You had a possible exposure to HIV either through vaginal or anal intercourse without the use of a condom or have been involved in any other risky sexual behavior.

  1. You have shared/reused needles or syringes to inject drugs (including steroids), or for body piercing, tattooing, or any other reason.

  1. You are a health care worker who's had a work-related accident such as direct exposure to blood or have been stuck with a needle or other object.

  1. You are uncertain about your sexual partner's risk behaviors or your sexual partner has tested positive for HIV.

  1. You are pregnant or are considering becoming pregnant.

  1. You have had certain illnesses including TB (tuberculosis), or an STI (sexually transmitted infection), such as syphilis or herpes.

  1. You have any reason to be uncertain about your HIV status.

If you have engaged in behaviors that have put you at risk of becoming infected with HIV, you may also have been exposed to other STIs. Some of these can be quite serious and require immediate treatment, such as syphilis or hepatitis C virus (HCV). If you are being tested for HIV you should also discuss with your provider whether you are at risk and should be tested for these STIs.



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