Patient information: Testing for HIV (Beyond the Basics)
- John G Bartlett, MD
John G Bartlett, MD
- Editor-in-Chief — Infectious Diseases
- Section Editor — HIV
- Section Editor — Pulmonary Infections
- Professor Emeritus
- Johns Hopkins University School of Medicine
HIV TESTING OVERVIEW
Human immunodeficiency virus (HIV) testing is used to determine if you are infected with HIV. Many individuals who are at the highest risk for HIV have not been tested, usually because they do not realize that they are at risk. Others avoid testing because they are worried about the possibility of a positive test result.
However, testing is encouraged because treatment for HIV is highly effective and early diagnosis can improve your chances of living longer and being healthier. Furthermore, knowing your HIV status can greatly reduce your risk of passing HIV to others if you take precautions.
WHAT IS HIV?
HIV is a virus that weakens your body's immune system, making it difficult to fight infections and certain cancers. People who are infected with HIV may have no signs or symptoms of their illness, but can still pass the infection to others through sexual contact or through exposure to contaminated needles. If HIV is not treated, you will eventually become very ill and may die. The advanced stage of HIV infection is called AIDS (acquired immune deficiency syndrome).
RISK FACTORS FOR HIV INFECTION
Nearly all HIV infections are acquired through sexual contact or exposure to contaminated needles.
You are at increased risk for getting HIV from sex if you:
●Had a sexually transmitted disease
●Had a sexual partner infected with HIV
●Were a victim of sexual assault (see "Patient information: Care after sexual assault (Beyond the Basics)")
●Are a man and had unprotected anal sex with another man
●Had unprotected sex with multiple partners
●Exchanged sex for money or drugs or have sex partners who do
You are at risk for exposure to HIV through contaminated needles if you have:
●Injected drugs with shared needles or "works"
●Been accidently stuck with a needle or sharp in a healthcare facility
Many people who have HIV have not been tested because they do not consider themselves at risk for infection.
Who should be tested for HIV — The Centers for Disease Control and Prevention recommends that everyone between the ages of 13 and 64 years be tested for HIV at least once. There are two reasons for this recommendation:
●The treatment of HIV is highly effective. People with HIV can live a nearly normal lifetime with currently available drugs. This treatment is most effective when it is started early in the course of the disease, before symptoms develop.
●Treating HIV can help prevent the spread of infection to others. If you know you are infected, you can change your behavior so you are less likely to put other people at risk.
TYPES OF HIV TESTS
Several tests can be used to diagnose HIV infection. Most involve testing your blood. The preferred tests are antigen-antibody tests. Antigens are foreign substances in the body (eg, a viral protein) that cause a response from the immune system. Antibodies are the proteins that the body produces to counteract antigens.
Antibody only tests — These tests detect the presence of antibodies that your body makes against HIV. If the antibody test is positive, the result is confirmed using another test called a “Western blot.”
Combination antigen-antibody tests — These tests detect both the presence of virus (viral antigens) and the antibodies your body makes against the virus. The combination antigen-antibody tests are better able to identify early HIV infection compared with antibody-only tests. A positive test is followed by a second test to confirm the result.
Tests that measure HIV RNA — Certain tests detect HIV in your blood by measuring HIV RNA (a part of the virus). When the test measures the level of virus RNA in the blood, the result is referred to as the “viral load.” In most situations, viral load testing is not better than routine antibody or antigen-antibody testing. Viral load tests can only detect certain types of HIV, and on occasion can give false positive results (ie, say that you have HIV when you do not).
HIV TESTING METHODS
HIV testing can be performed in different ways (eg, rapid verus standard), and in different settings (eg, in a doctor’s office or clinic versus at home). All positive screening tests should be confirmed with another test.
Rapid tests — Rapid tests for HIV use blood from a finger prick or oral fluids. These tests provide results within 5 to 40 minutes and are useful because they do not require that you go back on another day for your results. A positive result must be confirmed with additional testing. A negative test does not have to be confirmed.
Standard tests — The standard HIV test uses a sample of blood taken from a vein. These tests are performed in a laboratory, and the results are usually available in a few days.
Anonymous testing — Anonymous testing allows you to be tested without disclosing your identity, and is offered in some areas. To locate a clinic that provides anonymous HIV testing in the United States, call 1-800-750-2016.
Home testing — Home test kits provide accurate and anonymous results and are available in most pharmacies. One type of test requires a small sample of blood, which is obtained by pricking the finger. The blood is blotted on a filter strip and mailed to a lab. The lab performs the test and calls you with the result. The results of the test are confidential and are not reported to anyone but you.
Another home-based test, called “OraQuick,” uses oral fluids instead of blood. Positive results are generally very accurate. However, a negative result is not as reliable as a positive test since one in twelve tests will say the test is negative when the person actually has HIV.
HIV TESTING PROCEDURE
Frequency of testing — The Centers for Disease Control and Prevention recommend an HIV test for all people between age 13 and 64, and a repeat test if you have new risk factors, such as a new sexual partner. People who are at high risk for HIV, such as men who have sex with men, injection drug users, and those with multiple sex partners or a partner known to be HIV- infected should be tested every 6 to 12 months. (See 'Risk factors for HIV infection' above.)
If you think you were recently exposed to HIV and the initial test is negative or indeterminate, it should be repeated. A discussion of HIV testing in patients who were recently exposed to HIV is found below. (See 'Negative result' below and 'Indeterminate result' below.)
HIV TEST RESULTS
Test results are reported as being positive, negative, or indeterminate. The chances of having an inaccurate result are very small.
Negative result — If you have a negative blood test, you are unlikely to be infected with HIV.
However, if you were exposed to HIV recently (ie, within a few weeks), you should be retested. Diagnosing early HIV infection is important; that is the time when a person is most likely to transmit HIV to someone else since virus levels are high. The frequency and duration of follow-up testing depend on the type of HIV test being used (see 'Types of HIV tests' above):
●If an antibody-antigen test is negative, follow-up testing should be performed at six weeks and four months after the exposure.
●If an antibody test is negative, repeat HIV testing should occur at six weeks, three months, and six months following the exposure since it can take up to six months for your body to make antibodies to the HIV virus.
Positive result — If your first HIV test is positive, the result needs to be confirmed with further tests. False positive results are uncommon. About a third of patients who are tested for HIV do not return to find out their confirmatory test results. This is a major problem since untreated infection can lead to serious complications and a risk of transmitting infection to others.
Indeterminate result — An indeterminate result occurs when your result is not clearly positive or negative. The final result usually depends upon your risk of having HIV. In people at low risk for HIV infection, approximately 1 in 5000 results (0.02 percent) are indeterminate. Persons at high risk for HIV who have an indeterminate result may be in the early stages of HIV infection, and subsequent tests will be positive. Less often, a person who is basically healthy can have an indeterminate result for unknown reasons, and subsequent tests will be negative.
If you have an indeterminate result, you will need further testing, as determined by an HIV specialist; a viral load test may give an answer in just a couple of days (see 'Types of HIV tests' above). While awaiting the results of further testing, you should take precautions to avoid transmitting your potential infection to others. This includes discussing the possibility of infection with any sexual partners and use of a condom with every sexual encounter. You should also avoid sharing razors, toothbrushes, and any injection drug equipment (needles, syringes).
In addition to testing, you should learn how to prevent HIV infection. This includes:
●Encouraging your sexual partners to be tested for HIV
●Using a latex or polyurethane condom with every sexual encounter
●Avoiding drugs or alcohol that can affect your judgment about sexual activities
●Avoiding activities such as sharing needles and syringes that have been used by other IV drug users
To help prevent infection after a possible exposure to HIV, your provider may prescribe antiviral medications (ie, medications used to treat HIV). If you had unprotected sex or shared needles with someone who has (or is at risk for) HIV, these medications may reduce your risk of getting HIV. However, you must contact your doctor or nurse right away so you can start the medications as early as possible, preferably within three days of being exposed to the virus. In addition, if you are at high risk for getting HIV (eg, if you are a man who has sex with men, or are an injection drug user), you can ask your provider about “pre-exposure prophylaxis,” which means you take antiviral medications before, and not just after each possible exposure.
WHERE TO GET MORE INFORMATION
Your healthcare provider is the best source of information for questions and concerns related to your medical problem.
This article will be updated as needed on our web site (www.uptodate.com/patients). Related topics for patients, as well as selected articles written for healthcare professionals, are also available. Some of the most relevant are listed below.
Patient level information — UpToDate offers two types of patient education materials.
The Basics — The Basics patient education pieces answer the four or five key questions a patient might have about a given condition. These articles are best for patients who want a general overview and who prefer short, easy-to-read materials.
Patient information: HIV/AIDS (The Basics)
Patient information: Tests to monitor HIV (The Basics)
Patient information: Blood or body fluid exposure (The Basics)
Patient information: Preventing HIV after unprotected sex or needle-sharing (The Basics)
Beyond the Basics — Beyond the Basics patient education pieces are longer, more sophisticated, and more detailed. These articles are best for patients who want in-depth information and are comfortable with some medical jargon.
Professional level information — Professional level articles are designed to keep doctors and other health professionals up-to-date on the latest medical findings. These articles are thorough, long, and complex, and they contain multiple references to the research on which they are based. Professional level articles are best for people who are comfortable with a lot of medical terminology and who want to read the same materials their doctors are reading.
Professional Level Information:
Acute and early HIV infection: Treatment
Acute and early HIV infection: Pathogenesis and epidemiology
Initial evaluation of the HIV-infected adult
Screening and diagnostic testing for HIV infection
Techniques and interpretation of HIV-1 RNA quantitation
Nonoccupational exposure to HIV in adults
Pre-exposure prophylaxis against HIV infection
The following organizations also provide reliable health information.
●Centers for Disease Control and Prevention (CDC)
●CDC (Centers for Disease Control and Prevention) National AIDS Hotline
English: (800) 342-2437
Spanish: (800) 344-7432
●National Institute of Allergy and Infectious Diseases (NIAID)
●HIV/AIDS Treatment Information Service
Toll-free: (800) 448-0440
●AIDS Clinical Trials Information Service (ACTIS)
Toll-free: (800) 874-2572
Patient Support — There are a number of online forums where patients can find information and support from other people with similar conditions.
●About.com HIV/AIDS Forum
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All topics are updated as new information becomes available. Our peer review process typically takes one to six weeks depending on the issue.