The Top Ten Questions About HIV Tests
Are you considering being tested for HIV? Are you wondering what your options are, if you can be tested for free, and if you have to give your real name? Or have you received a test result and are now wondering how accurate it is? Welcome to “The Top Ten Questions About HIV Tests.” My name is [PRESENTER NAME]. I’m [PRESENTER ROLE]. In this video, we will explain the different kinds of HIV tests that are commonly used today, how accurate they are, and how you can be tested quickly, easily, and at no charge.
1) How Do HIV Tests Work?
HIV tests attempt to determine if you have been infected with HIV, the virus that causes AIDS. The most widely-used tests look for antibodies to HIV in your body. To keep the risk of an incorrect result as low as possible, you will normally have to be tested twice (once with an initial ELISA test, then a second time with a Western Blot if the ELISA's result was positive) before you are given a diagnosis of being HIV positive.
On the other hand, to be certain that you are HIV negative, you will have to test HIV negative at least six months after your last possible exposure to HIV.
2) What are the Window Period and False Negatives?
The two widely-used tests we mentioned already, ELISA and Western Blot, will only return a positive result after your body has created antibodies to HIV. That takes a while—as long as six months in some people. This is called the “window period,” during which standard ELISA and Western Blot tests may return a “false negative” result even though the person has actually been infected with HIV. This is why even if you get a negative test result, your doctor may tell you to come back in a few weeks or months to be tested again.
PCR Test: For Detection of HIV Infection During the Window Period
There is another test that can be used during this window period. It’s called the PCR test. PCR stands for Polymerase Chain Reaction. It’s a very sensitive test that looks for the presence of the virus itself in your blood, not the antibodies. PCR may be more expensive and doesn’t give you an immediate result, so it’s not generally used unless there’s a particular reason to do so.
The PCR test is very useful for diagnosing primary HIV infection. When people are initially infected with HIV, the virus multiplies very rapidly in the body because the immune system hasn’t had time to gear up a strong response and fight back yet. During this time, a person will have extremely high viral loads—up to 2 million copies of the virus per milliliter of blood—and they are by far the most infectious. In fact, it’s estimated that up to a third of HIV transmissions via sex occur during the period of primary HIV infection. During this time, 40-90% of people infected with HIV will experience signs and symptoms of primary HIV infection such as fever, sore throat, swollen lymph nodes, fatigue, rash, and flu-like symptoms.1 Watch our video “Did I Just Contract HIV? Symptoms of Primary HIV Infection” to learn more about how to recognize primary HIV infection.
If you think you might have been exposed to HIV, it’s important to get tested. If you think you’re experiencing primary HIV infection, it’s critical that you be tested for HIV right away. The PCR test can be used to determine that you’re infected with HIV even before your body makes antibodies and the ELISA and Western Blot tests will return a positive result. So if you think you’re experiencing primary HIV infection, go to the doctor. Tell them your risk factors, possible exposures to HIV, symptoms, and that you think you might be experiencing primary HIV infection. Ask whether the PCR test would be right for you. You may also request a referral to an HIV specialist or an infectious disease physician, either of whom will be more familiar with the use of PCR.
3) How long after exposure to HIV does it take for a person to test HIV positive?
According to the U.S. Centers for Disease Control and Prevention:2
Š On average, it takes 25 days for a person to develop antibodies to HIV that are detectable using the ELISA test.
Š “Most people will develop detectable antibodies within 2 to 8 weeks.”
Š “Ninety-seven percent of persons will develop antibodies in the first 3 months following the time of their infection.”
Š “In very rare cases, it can take up to 6 months to develop antibodies to HIV.”
Using a PCR test, HIV infection can be detected within nine to eleven days after exposure to HIV.
4) What's the Risk of a False Positive on the Initial ELISA Test?
The ELISA test is quick, easy, inexpensive, and fairly accurate, although not perfect. According to Roger Chou, M.D., and his coauthors in a study published in the Annals of Internal Medicine, "A large study of HIV testing in 752 U.S. laboratories reported a sensitivity of 99.7% and specificity of 98.5% for enzyme immunoassay (45) …."3 (which is another name for the ELISA).
That means two things. First, if a person is HIV positive, there is a 99.7% chance that the initial ELISA test will be sensitive enough to give a result of “HIV positive” as it should. Second, if a person gets an ELISA test result of “HIV positive,” there’s a 98.5% chance that their test result is correct.
What about the other 1.5%? If a person got an ELISA test result of “HIV positive,” but it is later established that they are not infected with HIV, we say that the ELISA test result was a “false positive.” False positive test results on the ELISA test do occur. Pregnancy, recent influenza vaccination, and autoimmune diseases like lupus are some possible causes of “false positive” ELISA test results.
5) What's the Risk of a False Positive Diagnosis After a Western Blot Test?
If a person gets a result of "HIV positive" on the initial ELISA test, the doctor will perform a Western Blot test to make sure that the first test wasn't a false positive. If the Western Blot also returns a result of "HIV positive," the person is given a confirmed diagnosis of being "HIV positive."
It is POSSIBLE for an HIV positive result on the Western Blot to be a false positive. However, this is EXTREMELY rare. According to Roger Chou, M.D. and his coauthors in the 2005 review in the Annals of Internal Medicine, “With confirmatory Western blot, the chance of a false-positive identification in a low-prevalence setting is about 1 in 250,000.”4
Dr. Chou's study showed that if a person gets a result of HIV positive on the initial ELISA test followed by a result of HIV positive on the confirmatory Western Blot test, there's only one chance in 250,000 that the person's diagnosis of "HIV positive" is a "false positive." In other words, if you get an HIV positive result on the initial ELISA and on the Western Blot, there is a 99.9996% chance that you are indeed HIV positive.
Videos and web site on the Internet by HIV denialists (people who claim that HIV isn't the cause of AIDS) often talk about "false positive" test results and exaggerate their frequency. They're usually talking about "false positive" results on the initial ELISA test, which may account for as many as 1.5% of total "HIV positive" results on initial ELISA tests. But a person is not given a diagnosis of being "HIV positive" until they've received an "HIV positive" test result on BOTH the ELISA and on the Western Blot. If you have taken both an ELISA and a Western Blot and your doctor tells you that you are HIV positive, believe them. The odds are overwhelmingly high at that point that you are in fact HIV positive.
6) Can I Be Tested for Free?
Yes. Just about anywhere in the world, if you can get to a public health clinic or Sexually Transmitted Disease testing center, you can be tested for HIV for free. Don’t let the fact that you don’t have health insurance or the inability to pay discourage you from getting tested for HIV.
7) Can I Be Tested Without Revealing My Name?
Yes. If you want to be tested for HIV but don’t want to reveal your name, there are several ways you can do this. Let’s talk about each one.
In some U.S. states and some countries, you can go to a public health clinic and tell them that you want to be tested for HIV anonymously. They will test you for HIV without recording your name.
Confidential, Name-Based Testing
Not all U.S. states and not all countries have this kind of anonymous testing program. Some U.S. states require that you provide a name when you are tested. They keep the name confidential and do not make it public. This is called “Confidential, Name-Based Testing.” If you don’t want to give your real name, you don’t have to. Don’t let confidential reporting requirements deter you from getting tested for HIV.
Home-Based Testing for HIV-1
There are two major types of HIV: HIV-1 and HIV-2. HIV-1 is the predominant type of HIV outside of Africa. Another way to be tested for HIV-1 is to use a home-based HIV-1 test kit that you can buy at any pharmacy in the U.S. and in many other countries as well. You don’t need a prescription to get the kit. You just go to the store, buy it, and take it home with you. At home, you follow its instructions to get a sample of fluid from your gums. You mail in your sample and then call a toll-free phone number to find out your result later. No one knows your name; you get your results using an anonymous code number from your test kit.
This approach is not free; you do have to pay for the test kit. But it’s anonymous, and you can do it right in your own home.
8) Do I Have to be Stuck With a Needle?
Not for the first test. The first test is usually done today with a simple oral swab or a finger stick. If you test positive on the first test, you will need to give blood for the second test, which is a Western Blot. But you only have to give a little bit of blood.
9) If I Test HIV Positive, Does That Mean I’m Going to Develop AIDS and Die?
It doesn't have to. People who are HIV positive can make wise choices that will improve their chances of living a long, healthy life even if they are HIV positive. If a person gets tested for HIV, learns they are HIV positive, and follows their doctor’s instructions, including the use of antiretroviral medications where appropriate, they may be able to prevent HIV from progressing to clinical AIDS for years, decades, or possibly for the rest of their life. See of video "Is HIV a Death Sentence?" for more information about why being diagnosed with HIV doesn't necessarily mean a person will develop AIDS or die from AIDS.
10) Why Should I Get Tested?
It's quick, easy, free, and your privacy is protected. If you're HIV negative, it will keep you from worrying needlessly. If you're HIV positive, it can save your life and the life of your sexual partners or unborn child. Health experts recommend getting tested, and you'll be doing your part in the global fight against HIV. Need more reasons? Watch our video "The Top Ten Reasons to Take an HIV Test." Get tested. It's the right thing to do. This is [PRESENTER NAME].
Script by Eric Krock and Becky Kuhn, M.D.
This script was reviewed for accuracy and approved by Becky Kuhn, M.D. on June 28, 2008.
Marcus Altfeld and Bruce D. Walker, “Acute HIV-1 Infection,” HIV Medicine, 14th Ed., 2006.
 Centers for Disease Control and Prevention, “How long after a possible exposure should I wait to get tested for HIV?,” accessed 27 June 2008.
 Chou et al, Annals of
Internal Medicine, 5 July 05, vol 143, #1, p 55-73.
 Chou, 2005.
“ELISA,” accessed 28 June 2008, http://en.wikipedia.org/wiki/ELISA_test
Gallant, Joel E., MD, MPH. "The HIV-Positive Patient: The Initial Encounter." 7 May 2002. MedScape Today. Accessed 28 June 2008.
"HIV test," http://en.wikipedia.org/wiki/Hiv_test
"Sensitivity and specificity," http://en.wikipedia.org/wiki/Sensitivity_(tests)
"Type I and type II errors," http://en.wikipedia.org/wiki/Type_I_and_type_II_errors
“Western blot,” accessed 27 June 2008, http://en.wikipedia.org/wiki/Western_Blot