Testing for the novel coronavirus (COVID-19) is increasing in many communities. But who actually needs coronavirus testing, and what types of tests are most accurate? What does the COVID-19 nasal swab test involve? And what does it mean if your test results come back negative?
We spoke with Micah Bhatti, M.D., to learn more.
How does COVID-19 nasal swab testing work?
The person conducting the test will insert a long stick with a very soft brush on the end — kind of like a pipe cleaner — up your nose and twirl it around for a few seconds. The soft bristles will collect a sample of secretions there for analysis. The swab has to go pretty far back, because cells and fluids must be collected from along the entire passageway that connects the base of the nose to the back of the throat to get a really good specimen.
The body is not used to having an object in that area, though, so it creates a lot of very odd sensations. For one thing, it activates the lachrymal reflex, which means it’ll bring tears to your eyes if it’s done correctly. Since the swab will also touch the back of the throat, it may also trigger a gag reflex.
Are there any other types of COVID-19 tests available?
Yes, tests can be performed on other specimen types that are less invasive, such as a throat swab. But they are less sensitive than the COVID-19 nasal swab test. Saliva is another specimen type that is being explored, but the jury is still out on that one. The preliminary data look really promising. But we’re still waiting on larger studies to confirm these initial findings.
In addition to nucleic acid testing, which detects a virus’ genetic material, there is also antigen testing, which detects the presence of viral proteins that spur the production of antibodies, or the immune system’s response to invaders.
While antigen tests are quicker, they are also much less sensitive than nucleic acid tests. So, while a positive antigen test is informative, a negative result would need to be confirmed by the more sensitive nucleic acid test.
It’s important to obtain the best possible specimens, so COVID-19 nasal swab testing that includes nucleic acid testing, which is what we do for our patients here at MD Anderson, remains the best option. After all, what’s the point of doing a test, if you can’t get an accurate answer?
What about at-home COVID-19 tests? Are their results reliable?
At-home tests typically involve an individual collecting their own specimen and then shipping it to a testing facility. While the prospect of testing for COVID-19 in the safety and comfort of your own home is quite appealing, the quality and reliability of these at-home test kits is still unknown.
There are concerns about the quality of specimens people collect on themselves, the integrity of the specimens during shipping, and the expertise of the lab where the testing will be performed. Until those concerns can be addressed, it’s best to have specimens collected by trained medical professionals and testing performed in certified labs that are trusted by your primary care physician.
What should I do if I think I need to be tested for COVID-19?
A COVID-19 nasal swab test must be prescribed by a doctor. So, if you think you might need to be tested for COVID-19, contact your primary care physician.
Is MD Anderson testing its cancer patients for COVID-19?
At MD Anderson, all new patients from out of state will be scheduled for a nasal swab COVID-19 test prior to their first appointment. We also take temperatures and ask screening questions of all patients when they arrive at MD Anderson. If we suspect they may have COVID-19, we will test them at that time.
We’re testing inpatients at admission, prior to discharge to a nursing or long-term care facility, and prior to procedures in the operation room, stem cell transplants, certain cellular therapy infusions, and procedures that generate respiratory aerosols or involve the mucous membranes, such as a colonoscopy or a Mohs procedure. We are also providing testing for patients when a household member has tested positive for COVID-19 in the last 14 days.
How accurate is COVID-19 nasal swab testing?
That’s both an easy and a difficult question to answer. The most commonly used test in all clinical laboratories is very sensitive. It’s called a “PCR assay,” which stands for “polymerase chain reaction,” and it is a specific type of nucleic acid test. It looks for traces of the coronavirus’ genetic material, which is what makes a virus do what it does.
In the lab, we can prove a PCR assay can detect very small amounts of the coronavirus. But when we move out into the real world, things get a little more complicated. The two main issues we’ve run into deal with specimen quality and viral load, or how much coronavirus is present in the body.
When you get exposed to COVID-19, it starts replicating in your upper respiratory tract. And the more coronavirus there is, the easier it is to detect. The plateau occurs pretty early on, within a few days of showing symptoms. But if we test you earlier than that, the results aren’t nearly as reliable.
Getting a perfect specimen is a challenge, too, because some collectors don’t feel comfortable inserting the swab as far as they need to go, and patients may jerk back. That’s why we’ve set up swab teams at MD Anderson to improve the quality of the specimens we get. These individuals are highly trained, specifically for the purpose of COVID-19 nasal swab testing.
What happens if my COVID-19 nasal swab test results are negative, but doctors still suspect I have the coronavirus?
First, they would look at your symptoms. Then, they’d consider additional testing, or whether your COVID-19 status could be determined using an alternative method, such as an X-ray.
The coronavirus often starts in the upper respiratory tract — where it causes symptoms like a sore throat, runny nose and dry cough. So, if you’re having those symptoms and they’re being caused by the coronavirus, a COVID-19 nasal swab test should come back positive.
But as it evolves, the coronavirus may move into the lower respiratory tract, where it can cause breathing trouble, a more productive cough and low oxygen levels in your blood. That’s when you might start needing oxygen or a respirator, so your lungs can do their job.
At that point, doctors might order imaging, like a chest X-ray or a CT scan of the lungs, to determine if you have COVID-19. If they see abnormalities that indicate an infectious process, then they’d weigh the risks and benefits of performing a more invasive procedure to obtain samples from inside your lungs.
One of those procedures is a bronchoscopy, where a fiber-optic camera is inserted down the throat and into the lungs to look around and collect samples. That is done only when absolutely necessary, because as with any other medical procedure, there are risks involved.
What are the chances that I might have a false-negative test result?
This is a common question, especially in light of the recent warning from the Food and Drug Administration regarding a high false-negative rate on certain tests.
It’s important to point out that a negative test result may occur in a patient who is in the early stages of the infection and shows no symptoms. A repeat test for this individual may well be positive, as the amount of virus in their body increases to detectable levels. If your physician feels the index of suspicion is high for COVID-19, they may order repeated testing to confirm the initial results.
What is MD Anderson doing to reduce the chances of getting a false-negative when running COVID-19 nasal swab testing for its patients?
The chances of a false negative at MD Anderson in a symptomatic patient due to a COVID-19 infection are very low, provided the lab receives a good-quality specimen.
MD Anderson takes several measures to ensure a low false-negative rate. First, we use a dedicated team of nurses to collect swabs, which ensures a high-quality specimen is collected every time. Second, the tests used in our laboratory have undergone a verification process to confirm that they perform as expected. And finally, we are tracking when repeat tests are positive on individuals who had previously tested negative.
To date, this last scenario has occurred in less than 1% of our tests. And, in all cases, the time between the negative and positive test results was more than 72 hours, opening up the possibility for infection to have occurred between the two tests’ administration.
I think I had COVID-19 before testing was available. Is there any way to confirm that I had it or that I’m immune to it now?
Not really. You can be tested for antibodies, but the results aren’t going to change how you’ll be treated if you’re a patient, or how you should conduct yourself out in the world.
Antibody tests, also known as serology testing, detect anti-viral proteins in the blood made by your immune system to neutralize the virus. But viruses have lots of different proteins and the antibody response can be very individualized.
Not everybody makes the same antibodies to a virus. So, a negative test result doesn’t necessarily mean you were not exposed to COVID-19. It could just mean the anti-viral proteins the test was set up to look for might not be the same ones your body made.
Similarly, even if I knew you’d had the coronavirus and generated antibodies, we simply don’t know enough to say that they would protect you against reinfection. We just can’t say that with any confidence yet. And as this coronavirus mutates — which all viruses do — antibodies to previous versions might not be effective anymore.
Finally, there’s the possibility that these tests may actually be detecting antibody responses to related or similar viruses. This coronavirus is just one of a much larger family of viruses that circulate regularly among humans. It’s something we’re still striving to unravel, so it makes interpreting antibody test results challenging.
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