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Even if you test negative for COVID-19, assume you have it, experts say

PCR tests being prepped
(Image: © Shutterstock)

Conventional diagnostic tests for the novel coronavirus may give false-negative results about 30% of the time, meaning people with an active COVID-19 infection still test negative for the disease, according to news reports.

"Unfortunately, we have very little public data on the false-negative rate for these tests in clinical practice," Dr. Harlan M. Krumholz, a professor of medicine at Yale University and director of the Yale New Haven Hospital Center for Outcomes Research and Evaluation, wrote in an opinion piece in The New York Times. However, preliminary research from China suggests that the most common type of COVID-19 test, known as a reverse transcriptase polymerase chain reaction (RT-PCR) test, may give false-negative results about 30% of the time.

The Chinese research has not yet been peer-reviewed, but anecdotally, Krumholz's colleagues have expressed concern that the false-negative rate may be even higher in the U.S., he wrote. 

"A lot of my patients who have symptoms, who I clinically think have COVID-19, are testing negative," Dr. Alain Chaoui, head of Congenial Healthcare, a practice with 50,000 patients across five locations in Massachusetts, told The Boston Globe.

RT-PCR tests work by detecting bits of viral genetic material present in a patient's mucus, saliva and cells at the very back of their nasal cavity, where the nose meets the throat, Live Science previously reported. Doctors collect patient samples using a long, skinny swab and then apply chemicals to the sample to eliminate everything apart from the viral genetic material, called RNA. Enzymes added to the sample jump-start a chemical process that transcribes the RNA into DNA, which can then be processed in a machine and copied many times over.

With enough DNA copies on hand, scientists can then apply fluorescent tags to the sample that bind to specific bits of genetic material and glow once attached. The glow announces the presence of SARS-CoV-2, the virus that causes COVID-19. 

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"The good news is that the tests appear to be highly specific: If your test comes back positive, it is almost certain you have the infection," Krumholz wrote. But RT-PCR tests might give false-negative results for a number of reasons, he added. 

In one scenario, the initial swab sample may not always collect enough genetic material to provide an accurate test. This problem may arise more often in patients who do not show many symptoms at the time of their test, the Globe reported. In addition, the standard nasopharyngeal swab, wherein a long instrument is wriggled and rotated to the very back of the nasal cavity, can be both difficult for clinicians to perform and uncomfortable for patients to endure, Krumholz wrote. 

Alternatively, false-negative results may result from how tests are processed in the laboratory or what specific chemicals are applied to each sample, Krumholz noted.

If false-negative results prove fairly common, what should people do if they receive one? 

Chaoui told The Boston Globe that he is advising all his patients who test negative for the virus to assume they are infected, regardless, and quarantine themselves until they are symptom-free for at least 72 hours. Krumholz shared a similar sentiment in the Times. At UMass Memorial Medical Center in Worcester, epidemiologist Dr. Richard Ellison told the Globe that the hospital is now retesting patients who received a negative test but have symptoms of the novel coronavirus, in an attempt to cut down on false negatives.  

"For now, we should assume that anyone could be carrying the virus," Krumholz wrote. "If you have had likely exposures and symptoms suggest Covid-19 infection, you probably have it — even if your test is negative." 

That said, no diagnostic test provides accurate results 100% of the time, and the tests developed by the U.S. Centers for Disease Control and Prevention are highly sensitive to the coronavirus, Dr. Larry Madoff, medical director of the Bureau of Infectious Disease at the Massachusetts Department of Public Health, wrote in a statement, according to the Globe.

"No test detects every case and there is no current 'gold standard' to compare [the COVID-19 tests] to," he wrote. "Testing may be falsely negative if the test is obtained too early or too late compared to infection, or if the sample isn’t obtained or processed correctly."   

Originally published on Live Science. 

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  • Hopsngrains
    This is one of the craziest, twisted, brainwashed ideas I've heard. No way should any of us who are healthy and having stayed at home for the last 40 days, assume we have the virus. This kind of thinking only advances fear, anxiety, and misunderstanding.

    Having said that, testing (in all it's forms) should continue to be expanded to provide Proof that those of us who are NOT infected or sick should continue to be able to gather and get back to work. I'd suggest a card signifying that a person is virus free.

    The people who clearly did not listen w/regards to stay at home, or social distancing orders over the last 6 weeks put all of us more at risk, AND extended our stays at home (away from work and play). Though there are always some who do not listen, or create issues, I'd really like to "expletive deletive" these people up.
    Reply
  • Caz
    Something quite different said here:
    https://thebridgelifeinthemix.info/…/evidence-covid-19-pand…
    Silver bullet 6
    The test currently used for diagnosing coronavirus infections, the so-called SARS-CoV-2 Coronavirus Multiplex RT-qPCR Kit, should only be used for research and not for diagnostics according to its makers. No wonder, since studies have shown to give 80% false positives. In other words it diagnoses inaccurately 8 out of 10 times, which means that Joe the plumber could do better than that.
    https://www.creative-diagnostics.com/sars-cov-2-coronavirus…
    Reply
  • chuckf
    The problem with the active, molecular, cotton swab up your nose test is even if you test negative... you can still get the virus later.

    Someone can drive up to a testing facility get tested, be negative at that moment. Drive down the road a bit, go in the grocery store, and get infected then.

    This is why the calls for widespread active-virus testing is a real head scratcher for me. Antibodies testing makes sense. I definitely understand that there's no real reliable antibodies test out there. But what would happen if we spent less time focusing on active-virus testing and more time on research and development of a reliable antibodies test?

    Can't do a reliable antibodies test? Then let's start focusing on the number of active cases that are really bad... as in people that have to be admitted to the hospital or into ICU because of this virus and quit trying to scare the rest of the public into thinking that this virus is some world-ending "Captain Trips" virus. I'm sure this virus isn't pleasant to deal with at home... but neither is the flu. Let's add a bit of perspective to this.
    Reply
  • Caz
    I now see that the expert who wrote this article is a cardiologist, not a virologist, not a microbiologist, not an epidemiologist.
    https://health.usnews.com/doctors/harlan-krumholz-196495
    Reply
  • harpat949
    admin said:
    No diagnostic test is 100% accurate, but experts have still expressed concern at the accuracy of the COVID-19 tests.

    Even if you test negative for COVID-19, assume you have it, experts say : Read more
    How do we know who is an expert?
    Reply
  • Caz
    expert: "a person who is very knowledgeable about or skilful in a particular area. "
    Harlan Krumholz's particular area is cardiology. Maybe he is very knowledgeable or skilful in this particular field.
    https://health.usnews.com/doctors/harlan-krumholz-196495
    Reply
  • Caz
    Since the tests are so unreliable, why is the army testing on the streets of Liverpool, UK:
    sRVgszShLYMView: https://www.youtube.com/watch?v=sRVgszShLYM
    update here: aEzkUxqv-8kView: https://www.youtube.com/watch?v=aEzkUxqv-8k
    Reply