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Photo of a home test kit for COVID-19 for an article about what to know about home testing if you're immunocompromised
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At the beginning of the coronavirus pandemic two years ago, the lack of available testing was a widespread issue. In many cases, if a health care professional suspected you had COVID-19 based on your symptoms but didn’t have a test available, you would be sent home and told to isolate.

Today, the wide availability of tests — including many types of at-home tests — provide one more layer of risk mitigation, especially for the immunocompromised and their family and friends. Asking your loved ones to get tested before you gather as a group or testing yourself at the very first sign of any symptoms (which can help you get treatment faster) can make a big difference in your risk level or severity of COVID-19 outcomes.

However, there’s also quite a bit of information floating around about at-home tests, including the best way to take them and their efficacy. Here’s the latest information you should know about at-home COVID-19 tests if you’re immunocompromised.

The Type of COVID Test You Take Matters

The two main types of at-home tests are 1) rapid antigen tests, which can provide you with results within 15 minutes, and 2) PCR tests, which you can take at home but need to send to a lab for results (which can take a few days).

If you have COVID symptoms or have a lot of virus in your system, antigen tests are very accurate. They can be less sensitive than PCR tests based on the situation. For instance, antigen tests can miss early cases of COVID-19, per UMass Chan Medical School.

On the other hand, the more sensitive PCR test may show a positive result long after you’re contagious, which makes it less helpful for “testing out” of isolation.  (See “Testing Out of Isolation Is Different for the Immunocompromised.”)

“Having a positive PCR strongly suggests that someone has been infected with the SARS-CoV-2 virus, but it doesn’t tell us anything about the extent to which that person is contagious,” says David Aronoff, MD, Chair of the Department of Medicine at Indiana University School of Medicine. “People can be SARS-CoV-2 positive on a PCR test for months after being infectious, including during times when they are absolutely not contagious.”

On the other hand, a positive antigen test should be interpreted to mean contagious.

“In general, a positive result from a rapid antigen test strongly suggests someone is infected and infectious — or in other words, contagious — because that test is detecting pieces of the outer viral shell that generally are only present in the airways like the nose when intact infectious virus is being generated,” says Dr. Aronoff. (See “When You Can Trust the Results — and When You Need a Second Test.”)

It’s Still Best to Swab to Your Nose

Some early reports have suggested that there may be a benefit to swabbing your mouth or throat for a COVID-19 sample, as opposed to your nose.

One preprint study (meaning it hasn’t been peer-reviewed yet) compared saliva and nasal rapid test sampling in 382 symptomatic, non-hospitalized patients who also had PCR tests done. The nasal rapid test results agreed with the standard lab-based PCR test for presence of the Omicron variant 86 percent of the time, while the saliva rapid test findings agreed with the lab-based tests 100 percent of the time.

Meanwhile, the positive percent agreement rates were 71 percent and 100 percent for nasal and saliva tests, respectively, for the Delta variant (similar results were found for the Beta variant).

The reason saliva testing isn’t widely recommended yet is because there isn’t a uniform way established to collect a sample. For instance, some of the many ways someone could collect a sample of COVID-19 from their mouth include:

  • Swabbing the throat with the swab tip
  • Saturating the swab with saliva
  • Rolling the swab in various parts of the mouth
  • Placing the swab under the tongue
  • Swabbing the inside of the cheek
  • Coughing a few times into the elbow (for deeper respiratory secretion) before taking the sampling

Because experts don’t know which method is the best for collecting a sample for SARS-CoV-2 detection yet, there’s no standardized recommendation — which can lead to more discrepancies with results.

“Different types of techniques for collection of secretion in mouth will yield different levels of performance, in terms of detecting SARS-CoV-2,” says Dr. Aronoff. “Some people may interpret getting a throat swab differently, which can lead to differences in the ability of these tests to outperform or underperform the currently approved nasal protocol.”

On the other hand, swabbing your nose is a little more clear-cut: Simply insert the swab into a nostril, circle it around a few times, then move on to the other nostril. (Follow the instructions with your home test for exactly what to do to get an accurate result.)

“Getting a good nasal sample, according to the instructions in a test kit, is likely to be less fraught with variation than telling people to get a sample from their mouth or throat without having a standard way to do that,” says Dr. Aronoff.

In short: Follow the instructions on the test kit, which will likely involve swabbing your nose. This may change in the future, but for now, it’s the best way to get dependable, consistent results.

Time of Day May Affect Your Test Results

If you have symptoms of COVID-19, you should get tested right away. However, if you’re asymptomatic and testing yourself as a precaution, it may be best to wait until midday.

A study from Vanderbilt University found that taking a COVID-19 test at the optimal time of day improves test sensitivity, which could be helpful in diagnosing people who are infected but asymptomatic. Researchers analyzed 86,342 clinical tests performed among symptomatic and asymptomatic patients in a regional health care network in the southeastern United States from March to August 2020.

They found evidence of “diurnal variation,” meaning there was the most sensitivity to detect viral infection around certain times of the day — namely late morning and afternoon — due to the way infected cells release viral particles into your mucus.

“It appears that the virus may be more likely to be present in the mucus in the middle of the day than at night,” says study author Carl Johnson, PhD, Cornelius Vanderbilt Professor of Biological Sciences at Vanderbilt University School of Medicine. “As people are now doing a lot of home testing, where it might be more convenient for them to do it before bed, it’s worth remembering that may not be the time of maximum sensitivity.”

But again, if you have symptoms, get tested as soon as possible. Certain COVID-19 treatments, like monoclonal antibodies or antiviral pills, are most effective when they’re taken within days of symptoms appearing.

If you were exposed to COVID-19, you should get tested at least five days after you had close contact with the infected person (even if you don’t develop symptoms), per the CDC.

Testing Out of Isolation Is Different for the Immunocompromised

In general, people who have moderate COVID-19 illness should isolate for 10 days (isolation can end at least five days after the first positive test for those who never develop symptoms, as long as they continue to wear a properly well-fitted mask around others for an additional five days), per the CDC. Read on to learn “how to find N95 masks if you’re immunocompromised.”

However, if you are moderately or severely immunocompromised, you may be less likely to fight infection and remain contagious for longer. Early in the pandemic, researchers found that immunocompromised people infected with COVID-19 often have especially severe and long-lasting infections, which leads to prolonged viral shedding (meaning they release the virus for a longer period of time), per Michigan Health.

According to the CDC, people are considered to be moderately or severely immunocompromised if they have:

  • Been receiving active cancer treatment for tumors or cancers of the blood
  • Received an organ transplant and are taking medicine to suppress the immune system
  • Received a stem cell transplant within the last 2 years or are taking medicine to suppress the immune system
  • Moderate or severe primary immunodeficiency (such as DiGeorge syndrome, Wiskott-Aldrich syndrome)
  • Advanced or untreated HIV infection
  • Active treatment with high-dose corticosteroids or other drugs that may suppress your immune response

The CDC recommends some people who are very immunocompromised — and may have a harder time fighting off the virus — may need to extend isolation to 20 or more days (day 0 is considered the first day of symptoms or a positive viral test).

You should use a test-based strategy and consult with your doctor to determine the right duration of isolation and precautions to take. This doesn’t apply to everyone who is taking immunosuppressant medication, as some people may be much more immunocompromised than others.

Part of that test-based strategy may involve taking an at-home test. In this case, it’s best to opt for a rapid antigen test.

“I would not recommend PCR testing to get out of isolation, because people can be positive by molecular tests for weeks or months beyond the point in which they are no longer contagious,” says Dr. Aronoff. “If it comes back positive, it’s not helpful in assessing their risk of spreading virus.”

On the other hand, a rapid antigen test that indicates your level of contagiousness can be helpful if you’re clearly feeling better and hoping to come out of isolation.

“It’s not at all unreasonable to use testing, like rapid antigen testing, if someone is clearly better and trying to come out of isolation after 10 days,” says Dr. Aronoff. “In that case, having two negative tests separated by 24 hours is really reassuring.”

Of course, it’s always best to review test results with your health care professional and determine the best next steps together.

When You Can Trust the Results — and When You Need a Second Test

At-home tests can also be helpful for getting results within quickly when you start to feel symptoms of COVID-19, which is particularly important if you’re immunocompromised.

“At-home tests are useful for immunocompromised people — if someone gets a rapid antigen test and it’s positive, they should either get a confirmatory test or assume they’re infected and isolate themselves,” says Dr. Aronoff.

In other words, if you receive a positive antigen test, that should be interpreted to mean you’re contagious.

But if your at-home rapid antigen test is negative, it’s important to know it doesn’t 100 percent rule out infection, adds Dr. Aronoff. If you are symptomatic but your rapid antigen test is negative, you should get a PCR test to confirm that negative result. If that test is negative, you could be symptomatic for reasons not related to COVID-19 (such as flu, a different respiratory infection, allergies, etc.)

At-home testing continues to be a helpful tool for gathering with groups. If you’re getting together with loved ones who are asymptomatic, asking them to take an at-home test first is a good way to ensure you’re not walking into a potentially infectious environment. Your loved ones should take the test within three days of meeting with you, says Dr. Aronoff. That said, the sooner someone can test before a gathering, the better — even if it’s 15 minutes beforehand.  (And of course, if anyone has symptoms of COVID-19 or another infection, they should stay home.)

“Even though all testing is imperfect, any type of testing before people gather is useful if they are applying testing in addition to other mitigation methods to reduce the likelihood of an outbreak in association with gathering,” says Dr. Aronoff.

For instance, if you’re gathering as a group, you may choose to wear a mask (even outdoors) if you live in an area of substantial or high transmission — particularly if you have a weakened immune system or are at increased risk for severe disease, per the CDC. Keep in mind that almost all of the United States has “high” community transmission right now.

The Bottom Line

At-home tests continue to be an effective tool for screening yourself (or those you may meet up with) for COVID-19. Follow the instructions on the test kit and consider testing yourself at midday if you’re asymptomatic and simply using it as a screening tool. Otherwise, get tested as soon as you have symptoms.

If you are symptomatic but your rapid antigen test is negative, you should get a PCR test to confirm that negative result.

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Interview with Carl Johnson, PhD, Cornelius Vanderbilt Professor of Biological Sciences at Vanderbilt University School of Medicine

Interview with David Aronoff, MD, Chair of the Department of Medicine at Indiana University School of Medicine

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Quarantine and Isolation. COVID-19. U.S. Centers for Disease Control and Prevention. January 27, 2022. https://www.cdc.gov/coronavirus/2019-ncov/your-health/quarantine-isolation.html.

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