Interpretation of Negative HIV Test

Understanding Whether a Negative HIV Test is Always Really Negative

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 — either HIV negative or HIV positive. But there is a scenario when a negative HIV test may not be all that it appears. So when can HIV negative not mean HIV negative?

There is a short window period that a person can test HIV negative and still be HIV infected. When HIV initially infects the body, a person's immune system begins to develop antibodies to the virus.

It's those antibodies that most rapid HIV tests detect.

But 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 negative, when in fact she is HIV infected.

It's for this reason that doctors recommend a series of HIV tests — a test soon after an exposure, and an HIV test 3 months after the exposure. Some doctors will also recommend another HIV test 6 months after the exposure.

If all the tests are negative, and a person has had no new HIV exposures, they are considered to be HIV negative. 

If a person has another exposure during their series of tests, the tests need to be repeated, starting over from the point of the new exposure.

While a person is waiting for the series of tests to be completed, she should abstain from sex, use condoms during every sexual encounter, and not share injection drug needles or equipment.

 

Testing Caveats

Please note that other HIV tests —like RNA tests or antibody/antigen HIV tests — may have shorter window periods. Speak with your healthcare provider about whether and when you need to be retested based on the specific HIV test that was used. 

For instance, the CDC now recommends initial testing for HIV with an FDA-approved antigen/antibody combination immunoassay that detects HIV antibodies and HIV-1 p24 antigen — which is a protein made by HIV.

If this test is negative, than no further testing is needed.  

This all being said, rapid HIV tests are still commonly used in clinics and at home — and they test for HIV antibodies. For example, the FDA approved the first rapid home-use HIV kit, called the OraQuick test. It tests for HIV antibodies from a person's saliva, and results appear within 20 to 40 minutes. But due to the window period, the OraQuick test will produce approximately one false negative result out of every 12 tests performed in people infected with HIV. 

What Can I Do?

Go to a doctor or an emergency room and get tested right away if you think you have been exposed to HIV. You can also get post-exposure prophylaxis, an HIV medication that decreases your risk of developing HIV. 

Sources

Centers for Disease Control and Prevention. (2014). Laboratory Testing for the Diagnosis of HIV Infection: Updated Recommendations. Retrieved October 7th 2015.

Centers for Disease Control and Prevention. (2015). HIV/AIDS: Testing.  Retrieved October 7th 2015. 

U.S. Food and Drug Administration (FDA). (2013).  "First Rapid Home-Use HIV Kit Approved for Self-Testing." Retrieved October 7th 2015.

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