If you have recently been tested for HIV or if you are thinking about getting tested, you may be concerned about receiving a false reading. A false positive can be terrifying. Yet, a false negative can deter you from receiving much needed treatment and keep you from taking proper precautions to reduce the risk of transmission. That said, while false readings can create a lot of chaos, the truth is that they are rare.
Due to advancements in technology and testing, today’s methods of testing for HIV are highly accurate. Moreover, most testing facilities administer multiple tests for the purposes of reducing the chances of false readings, as each subsequent test can confirm the results of the preceding one. As a result, incorrect readings are very uncommon. However, that does not mean they do not occur.
HIV testing is highly accurate, with negative readings boasting a 99.9% accuracy rate. For both positive and negative results, HIV tests are 99.6% accurate when they are administered within the three-month window. That said, a few factors may affect the accuracy of HIV tests:
The first factor is the most influential factor in false readings. In the early stages of HIV, the virus is considered “acute,” meaning the viral loads are low. As a result, it is difficult to detect. However, as the virus becomes “chronic”—which occurs after several months—it becomes much easier to diagnose.
For an HIV test to deliver the most accurate result possible, it must be delivered within the “window period.” The window period is the period of time between exposure and when testing can detect the virus’s presence in the body. If a person tests before the window has closed — typically after three months of exposure — there is a strong chance one or several tests will produce a false negative.
While most HIV tests are most accurate long after the window has passed, some tests have shorter window periods. If you decide to use these tests, it is still important to follow up with additional tests after the standard window period has lapsed.
A false positive HIV test result is one that reads positive even though the tested person does not actually have the virus. False positives can occur for several reasons. Regardless of why they happen, though, false positive HIV tests can cause significant emotional duress, not to mention adversely impact the tester’s relationships.
That said, it is rare for a person to go on living with the emotional impact of a false positive for long, as most doctors will order additional tests if one or even two come back with a positive reading. Typically, the most significant backlash from a false positive occurs when a person tests at home but then never schedules follow-up testing to confirm the home test’s accuracy.
As previously mentioned, false positive results on an HIV test can occur for several reasons. The most common reasons for inaccurate positive results are as follows:
Other conditions that may trigger false positives on other types of HIV tests include prior pregnancy; a recent vaccination, such as for hepatitis B or flu; receiving multiple blood transfusions; receiving gamma globulin or immunoglobulin; and participation in an HIV vaccine study.
Other types of tests that can produce inaccurate results are the finger prick and oral fluid tests. Though accurate more often than not, these tests are not as reliable as blood tests.
Finally, a 2018 study showed that, while home-tests are highly accurate, many home testers collect the incorrect specimen. Incorrect specimen can trigger inaccurate results.
A false negative HIV test is one that delivers a negative result despite the person tested being positive for the virus. False negatives are far less common than false positives, as only one factor can really influence a false negative.
False negatives typically only happen when a person tests for HIV too soon after exposure. Remember, for the antibodies to be detectable in a person’s system, at least three months must have lapsed between exposure and testing. This gives the antibodies time to build-up to the point where they cannot avoid detection. Though the window does vary from test to test, most health organizations recommend that persons who were tested within the three-month window and who received negative results get retested after the three months has passed.
That said, there are some antibody/antigen tests that can detect even small viral loads much sooner than after three months. Many of these advanced tests can detect HIV within just 45 days of exposure. However, even though these tests have high accuracy rates, health organizations still recommend additional testing after three months just to confirm the first test’s results.
As with false positives, technical or clinical errors or a faulty test may also contribute to false positives.
There are three different types of HIV tests available. Each type checks for different signs or symptoms of the virus. Some are able to detect the virus sooner after exposure than others.
The most common type of HIV test is the antibody test. When the body comes into contact with a virus or bacteria, it produces antibodies to protect itself against the invader. Antibody tests can detect the HIV virus in saliva or blood.
For antibody tests to be accurate, the body must have enough time to produce enough antibodies for a test to detect them. Typically, antibody levels build up to detectable levels within three to 12 weeks of exposure. However, for some people, it takes longer, which is why health organizations recommend testing after the three-month window has lapsed.
Antibody tests fall into two distinct categories: rapid and regular. Rapid antibody tests are typically performed on blood or saliva, which are collected through finger sticks or venous blood draw. Results from finger sticks or saliva are usually available within 30 minutes, while results from venous blood draws are available more quickly. Finger stick and saliva tests are available for both clinical use and home use.
With standard antibody tests, it usually takes several days for results to become available. These tests require a doctor or health professional to draw a blood sample and send it to a lab for analysis.
The second type of HIV test is the antigen/antibody test. These tests are actually a series of tests or fourth-generation tests that detect antigens (proteins) from HIV and antibodies. When a person contracts HIV, the body will produce a protein called p24 before it begins to produce antibodies. Because of this, the antigen portion of the test can usually detect the virus long before the antibody test can.
With antigen tests, the window from the point of exposure to the stage at which detection is possible is usually much shorter than with antibody tests. Antigen tests can typically detect levels of p24 within 18 to 45 days (or two to six weeks) of first exposure. As with antibody tests, the window may be longer for some people.
Antigen/antibody tests fall into the “standard” category, meaning results are not available immediately. Rather, it may take several days for a lab to return results.
The nucleic acid test, or NAT, is a test that can detect genetic material from the virus in blood. This test is also known as an HIV RNA test.
NAT tests have the shortest detection window of all three types of tests, with most tests able to pick up traces of the virus within just 10 to 33 days of exposure. However, NAT is very expensive, making it one of the least popular and least practical options for vulnerable populations. It is also not a common screening tool unless a patient specifically requests the NAT, recently experienced a high-risk exposure incident or is experiencing acute symptoms of HIV infection.
Though highly accurate, NAT results can be skewed by postexposure prophylaxis or preexposure prophylaxis medications. If you have been taking PEP or PrEP, tell your doctor before he or she orders a NAT.
Ideally, individuals will get screened for HIV during each routine health check-up. Many individuals who recently engaged in risky behaviours may also request an HIV antigen or antibody test. Health organizations also recommend that persons between the ages of 13 and 64 get screened at least once.
For individuals who engage in risky behaviours or who live in more vulnerable populations, the recommendations are different. Individuals who have multiple sexual partners, use intravenous drugs or engage in other high-risk behaviours should undergo testing as often as everything three months. Frequent screening is necessary for your own protection and the protection of others.
If your first HIV test is positive, your doctor will order follow-up tests to confirm the diagnosis. This is the case regardless of whether your first test was an at-home antibody test or an in-office antigen test. Your doctor may also look for other conditions or circumstances that may result in a false-positive, such as the existence of an STI or certain medications in your blood stream.
If a viable reason for a false-positive does not exist, and if your second test comes back positive, your doctor will then begin to explore with you management and treatment options. The sooner you begin treatment, the less likely you are to develop complications and the better your long-term prognosis stands to be.
Typically speaking, the chances of an HIV misdiagnosis are low. HIV testing is highly accurate these days, with error mostly occurring when certain factors are present. However, if you think you received a false positive or a false-negative, seek follow-up testing. Just as importantly, consult with your doctor regarding ways you can protect yourself and long-term health going forward.