WebMD BlogsPublic Health

'Can a COVID-19 Test Be Wrong?'

COVID test car
By Elizabeth Hanes, BSN, RNOctober 12, 2020
From the WebMD Archives

You’ve been feeling lousy -- and since you’ve heard that just about any symptom could be a sign of COVID-19, you do the smart thing and get tested. To your surprise, the test comes back negative.

Negative? But I feel horrible! Could the test have been wrong?

Yes, that’s possible. 

COVID-19 tests, whether a rapid antigen test or a PCR test sent to a lab, do tend to be accurate on the positive side (if the test says you have COVID, you most likely do), but they can sometimes deliver false-negative results, especially the antigen (rapid) tests. Meaning, if the results are negative, there could still be a chance you have COVID-19. If you get a false-negative result, you could end up spreading it to other people while thinking that you’re in the clear.

A few reasons false-negative results might occur:

  1. A person gets tested before enough viral particles have accumulated in the nasal passages for the test to detect them. In general, most people who are infected with SARS-CoV-2 won’t test positive until several days (or even a week) after infection.
  2. The swab test was not administered correctly, and thus did not pick up enough secretions from the nasal passages to deliver an accurate result.
  3. The sample you gave with the swab or spit got contaminated.
  4. The swab wasn’t kept at the right temperature before getting analyzed.
  5. The chemicals used in the test didn’t work properly.

The timing aspect seems to be particularly important here. Looking at the most commonly used type of COVID-19 test (the PCR test, typically done with a swab), researchers found that the test can return a false-negative result as often as 67% of the time during the first 4 days of an infection.

So what does all of this mean? First, if you got a negative result from a rapid antigen test, consider getting a PCR test because it’s more accurate at detecting the virus. Second, if you feel sick you should act as if you have COVID-19, no matter what the test results say. That means isolating yourself at home for 10 days (if you live with other people, wear a mask in your home and stay as far away from others as possible, in a separate room if possible) and calling your doctor to report your symptoms and get personalized guidance about what to do next.

If you got a test because you were exposed to someone with COVID-19, but you don’t have symptoms, you shouldn’t assume a negative test result means you can go back to normal life. Instead, you should get retested (with a PCR swab) within a few days (especially if you develop symptoms), and you should quarantine for 14 days.

On the other hand, if you got a test for no particular reason and it’s negative, then it’s probably safe to go on about your business while taking the usual precautions: wear a mask, social distance, and wash your hands frequently.



WebMD Blog
© 2020 WebMD, LLC. All rights reserved.

More from the Public Health Blog

  • vitamin d supplement

    'What's the Best Time of Day to Take Vitamins?'

    Knowing what time of day to take your vitamin and mineral supplements can help you maximize their effectiveness and avoid dangerous interactions.

  • man sore throat

    'Does a Sore Throat Mean I'm Sick?'

    If your only symptom is a sore throat, it may not be anything to get worked up about. But, how do you know if you need to call a doctor?

View all posts on Public Health

Latest Blog Posts on WebMD

View all blog posts

Important: The opinions expressed in WebMD Blogs are solely those of the User, who may or may not have medical or scientific training. These opinions do not represent the opinions of WebMD. Blogs are not reviewed by a WebMD physician or any member of the WebMD editorial staff for accuracy, balance, objectivity, or any other reason except for compliance with our Terms and Conditions. Some of these opinions may contain information about treatments or uses of drug products that have not been approved by the U.S. Food and Drug Administration. WebMD does not endorse any specific product, service or treatment.

Do not consider WebMD Blogs as medical advice. Never delay or disregard seeking professional medical advice from your doctor or other qualified healthcare provider because of something you have read on WebMD. You should always speak with your doctor before you start, stop, or change any prescribed part of your care plan or treatment. WebMD understands that reading individual, real-life experiences can be a helpful resource, but it is never a substitute for professional medical advice, diagnosis, or treatment from a qualified health care provider. If you think you may have a medical emergency, call your doctor or dial 911 immediately.

Read More