What Does a Negative HIV Test Result Mean?

Does It Really Give Me the "All Clear" Sign?

Lab technician putting blood sample on a slide for HIV testing
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One would imagine that an HIV test would be fairly cut and dry, with the results either being HIV negative or HIV positive. HIV negative means you have no signs of HIV in your blood. HIV positive means that you do and have been infected with HIV.

But there is a scenario when a negative HIV test may not be all that it appears. When testing for HIV, there is a short window period when a person can test negative and actually have the virus in his or her system.

 

And the reasons are simple: when HIV infection occurs, a person's immune system begins to develop specialized proteins called antibodies, which are specific to the individual pathogen it aims to neutralize (in this case HIV). It is those antibodies that most antibody-base HIV tests detect.

But the simple truth is that it takes some time for enough of those antibodies to be produced for an HIV test to detect them. Therefore, if too little HIV antibody has been produced when a person gets tested, the test result will be returned as negative despite the fact that an actual infections has occurred.

How Do I Know for Sure That My Test Is 100% Negative?

In order to be sure that HIV infection has not occurred, doctors had traditionally recommended a series of HIV tests, with an initial test taken soon after exposure with another three months taken three months after the exposure. Some doctors will also recommend another HIV test six months after.

If all of the tests are negative, and a person has had no new HIV exposures, then they are considered to be HIV negative and clear of infection. However, if a person has another possible exposure to the virus between tests (such as condomless sex or shared injecting drug use), the tests will need to be repeated, starting over from the point of the new exposure.

Newer testing assays, employing combination antibody/antigen detection, are far more accurate and sensitive than older generation antibody tests. These are more capable of detecting HIV during the early, acute stages of infection, shortening the window period by as much as month.

These test work by detecting the HIV-specific proteins called antigens, which initiate the immune response and are therefore produced more rapidly after infection than antibodies.

For these types of tests, the Centers for Disease Control and Prevention (CDC) in Atlanta has determined that a single antigen/antibody test taken within the window period is enough to confirm a HIV negative result. No further testing is required.

Testing Caveats

Please note that while many of the newer HIV tests — like RNA-based tests or aforementioned antibody/antigen tests — may have shorter window period, their accuracy and sensitivity can vary, sometimes considerably. Even among the combination assays, some are known to be 87 percent accurate during acute infection with others top out at 54 percent.

Always speak with your healthcare provider about when you need to be tested and if retesting may be needed to provide greater confidence in the results.

With all this being said, rapid HIV tests are still commonly used in clinics and at home, and they test for HIV antibodies. In 2012, the U.S. Food and Drug Administration (FDA) approved the first rapid home-use HIV kit called the OraQuick, which is available in most retail drug stores today.  These in-home tests aim to detect HIV antibodies from a person's saliva, the results of appear within 20 to 40 minutes.

But unlike similar tests given at clinics and hospital, the in-home version will produce approximately one false negative result out of every 12 tests performed. If the test is performed incorrectly or too soon, the likelihood of a false result will only be greater.

If using an in-home test, don't take any chances. Contact the 24-hour helpline listed on the package insert if there are any questions, doubts, or concerns about the accuracy and use of the device.

What Can I Do If I Have Just Been Exposed to HIV?

 If you think you have been exposed to HIV, go immediately to a doctor or an emergency room and get tested right away. You can be provide post-exposure prophylaxis, an HIV medication that may decrease your risk of developing HIV, ideally if started within 48 hours of an exposure. 

Sources:

Centers for Disease Control and Prevention (CDC). "Laboratory Testing for the Diagnosis of HIV Infection: Updated Recommendations." Atlanta, Georgia; updated June 27, 2014. 

U.S. Food and Drug Administration (FDA). "First Rapid Home-Use HIV Kit Approved for Self-Testing." Rockville, Maryland; issued June 3, 2012.

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