The Basics of HIV

Getting Tested for HIV

by Dr. Jason Faulhaber
Fenway Community Health Center, Boston MA
EDGE Medical Correspondent

It is estimated that 1 in 5 individuals infected with HIV do not even know that they have it. How is that possible? Not everyone gets tested, routinely or at all. Most people infected with HIV do not show any signs or symptoms, especially early in the infection. Some people do not return for the test results, assuming that they would be contacted if they tested positive. Some people do not think they are at risk for becoming infected. Whether you have had 1 sexual partner or over 1000, you could be at risk for acquiring HIV. If you have ever shared a needle (whether for injecting drugs or getting tattoos), knowingly or not, you could be at risk.

There are several different tests available, and you should be aware of which one is being performed. You should also have a basic understanding of how these tests are done and what the results mean.

General Principles

All HIV testing in the United States is confidential, meaning that your name is used as an identifier for the sample but your name will not be shared with anyone without your consent. Some testing sites offer anonymous testing, meaning that you do not even have to provide your name. You get an identifying number which is used to obtain the test results.

Based on the recommendations of the Centers for Disease Control (CDC) that anyone who is sexually active between the ages of 13 and 64 should be tested, nearly all health insurance companies provide complete coverage for HIV testing. Some centers offer free testing, which is highly advantageous to those without health insurance as well as to those who do not wish to use their health insurance. You should know in advance if the testing is free or if it will be billed to your health insurance.

The Test Itself

The test is broken down into 2 stages: screening test and confirmatory test. Both tests look for antibodies to HIV, not for the virus itself. The screening test is a preliminary test used to determine if there may be antibodies present in the sample. If a screening test is positive, then a confirmatory test is used to determine if the antibodies are specific to HIV. If the screening test is negative, then no further testing is done.

Since the test is looking for antibodies to HIV, your body needs to generate those antibodies. Your immune system is continually surveying your body attempting to find foreign pathogens, such as viruses and bacteria. Once a foreign invader has been identified, the immune system kicks into high gear to attempt to control and eradicate the invaders. One way it does this is through antibodies. Antibodies are proteins in your body that coat the invader and signal other parts of your immune system to destroy the invader. Your immune system retains a memory of these antibodies so it may be able to fight them again in the future. The length of time it takes for the immune system to generate these antibodies depends on the invader. For HIV, the length of time could be 2-6 weeks, or even longer in some people. Consequently, a test looking for antibodies to HIV may not be able to detect them early on in infection.

If there is concern for acute infection—that you may have become infected with HIV within the past 6 weeks—then a different type of testing needs to be performed as the antibody test will likely be negative (since your immune system has not had sufficient time to make the antibodies to HIV). This test is called a “viral load,” which is looking specifically for the amount of HIV in the blood.

Types of Tests Available

With advances in scientific research, the waiting time for results of HIV antibody testing can be as short as 20 minutes. These are called “rapid” tests. These tests are only screening tests. They are available only in certain locations. If the rapid test is positive, a separate confirmatory test needs to be conducted. The confirmatory test can take 3 days up to 2 weeks, depending on the lab performing the test.

The rapid test can be performed on either blood or oral fluid. Many testing sites have chosen to test blood because of better accuracy of test results. The blood testing is often done on a finger prick, using a small sterile lancet such as that used in testing blood sugar. If the rapid test is negative, no further testing is performed at that time. If the rapid test is positive, then a separate blood sample must be obtained to be analyzed for the confirmatory test.

Conventional antibody testing utilizes blood samples only. This test is sent to a lab where they will perform the screening test first and then automatically do the confirmatory test if the screening test is positive. If the screening test is negative, then the confirmatory test is not done. The advantage to this type of testing is that it only requires getting stuck once with a needle.

There is a home sample collection kit available at certain pharmacies. The only one licensed by the FDA is the Home Access HIV-1 Test System. The kit contains the necessary equipment for you to conduct your own finger-prick, place drops of your blood on a testing card, and then submit the card to a licensed laboratory for analysis. You are identified only by a specific number attached to the collection kit. You can call in for the results and speak with a counselor live before testing and after receiving the results. It takes at least 3 days for the results to become available. Things to remember about using this testing method: your blood is perishable, so the package with your testing card needs to be received by the lab within a specific timeframe; you are responsible for acquiring the blood for testing; the package may get lost; it may cost more money than other testing options; and, if positive, it is recommended to obtain a separate confirmatory test.

The viral load testing can only be performed on a blood sample, and results may take up to 2 weeks to return. This test is not used for routine screening; it is only used if there is a high suspicion for acute infection (see above).

Limitations

As previously mentioned, one main limitation is the accuracy of the test result in relation to the time of exposure. If there has been a possible exposure within the past 6 weeks, then antibody testing may be negative. This would be an example of a “false negative” test result, meaning that you are infected but the antibody test was negative. In general, the current tests available have an accuracy of approximately 99.6-100% in detecting antibodies outside of the period of recent infection. The test also detects a certain concentration of antibodies in the sample; some people may take longer than 6 weeks in order to make enough antibodies to be detected. There also are very rare instances of “false positive” test results. The “false positive” test results may detect antibodies to an invader that is similar to HIV but not actually HIV. There also could be an error in the testing itself, whether performed by the testing counselor or the lab personnel. Another possible cause is participation in an HIV vaccine trial; if you have been in one of these trials, then you should not have rapid or conventional antibody testing done.

Interpretation of Results and Follow-Up

Negative. This means that the test did not detect antibodies to HIV, known as HIV-negative. If you have had any recent potential exposure, then it is recommended to be retested about 6-12 weeks later. If you have not had any possible recent exposure, then routine screening is recommended based on your overall risks (e.g., sexual partners, encounters with needles).

Positive. Not all positives are the same! If the rapid test is positive, this does not necessarily mean you are infected with HIV. A confirmatory test, which may take a few days, needs to be conducted to determine if you have antibodies to the virus. If the confirmatory test is negative, then it is recommended to repeat testing in about 6 weeks. If the confirmatory test is positive, this means that you have antibodies to HIV, known as HIV-positive. Other tests—like the viral load—would then be performed to determine if you are infected with HIV. No test can determine when you became infected; there may be ways to estimate the timeframe of infection, but it may be difficult to pinpoint an exact time.