Rapid COVID-19 Tests: When to Use Them and How They Work

Rapid antigen tests can be useful to determine if you have an infection, but the timing and frequency could be key for accurate results.

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  • Demand for antigen tests has soared since workplaces and schools have reopened and travel has resumed.
  • President Biden recently announced that rapid at-home COVID-19 testing will become much more widely available in the United States, making it easier and cheaper to access.
  • Pricing for antigen tests currently ranges between $5 and $50, and they give results in up to 30 minutes.
  • Although they are not quite as accurate as lab-based PCR tests, rapid antigen tests have comparable accuracy in symptomatic COVID-19 cases.

By December 2021, 200 million rapid tests are expected to be available to Americans each month as part of a drive to make community testing more widespread and accessible.

The announcement came last week with the White House signaling a billion-dollar investment in at-home rapid coronavirus tests.

It also said 20,000 pharmacies across the country would offer free testing starting from September.

We break down what these tests can do, the best times to do them, and list some of the most popular ones on the market.

What are rapid antigen tests?

Rapid tests for COVID-19 are a fast and easy method to detect the coronavirus. They are similar to a pregnancy test in the sense that they display one or two lines to indicate a result after a few minutes.

If the test detects viral antigens, which are a type of protein on the surface of the virus, it will show positive.

“Rapid tests are are a snapshot of how much virus you are shedding, if any,” said Eric Cioe-Peña, MD, director of global health at Northwell Health in New Hyde Park, New York.

He pointed out a caveat with these tests, it’s possible that if you have been exposed to COVID-19 the coronavirus could be building up in your body and eventually you will start to become contagious.

A negative result indicates that you likely do not have the infection at that moment in time.

“If the [result] is negative, it is usually pretty safe to engage in whatever event you are thinking about engaging in,” Cioe-Peña told Healthline.

How accurate are rapid antigen tests?

If you present with COVID-19 symptoms, and want to see if you have the disease, rapid tests are quite reliable and can offer similar accuracy as polymerase chain reaction (PCR) tests processed in labs. Studies have shown that antigen tests have comparable sensitivity to lab tests.

The current “gold standard” for clinically diagnosing COVID-19 is laboratory-based nucleic acid amplification tests (NAATs). Loop-mediated isothermal amplification (LAMP) and PCR tests are the most commonly used NAAT techniques.

While both lab-based tests such as PCR and at-home rapid antigen tests detect current infection, the former looks for viral ribonucleic acid (RNA) instead of viral antigens.

The sensitivity of rapid antigen tests can change depending on the course of infection and viral load. A higher viral load, which is usually a few days after infection, usually gives the most accurate results.

If rapid tests fail to detect enough antigens, they may produce a false negative. This can be because either the test was administered before symptoms appeared or the level of antigens was below the lowest limit the test could detect.

The advantages of rapid tests are that they are cheaper, take less time (compared to 1 or 2 days for PCRs), and are more widely accessible.

Who should get tested?

People who have symptoms of COVID-19, regardless of vaccination status or history of infection, should get tested, according to the Centers for Disease Control and Prevention (CDC).

If you suspect you have been in close contact with someone who had COVID-19, meaning, you were within 6 feet of a person with a confirmed case for 15 minutes or more, it would be a good idea to get tested.

People who have tested positive for COVID-19 within the past 3 months and have recovered do not need to get tested if they do not develop new symptoms.

Anyone who suspects they might have developed COVID-19 can do a rapid antigen test.

When is the best time to do a rapid antigen test?

The CDC says antigen tests perform best in symptomatic people and within a certain number of days after symptoms appear.

If you know you have been exposed to COVID-19, the Food and Drug Administration (FDA) recommends testing 3 to 5 days after exposure.

Cioe-Peña says the best time to test is the same day you want to know if you have the infection.

“Ideally, people should test using rapid antigen tests on the same day that they want to know whether they have an infection or not. The nice thing about rapid antigen tests with the Delta variant is that there are high concentrations of virus when you are shedding particles, so they are likely to turn out positive.”
– Eric Cioe-Peña, MD

In addition, experts say it may be a good idea for people to do rapid tests before going to work or school, visiting family or friends, or attending large gatherings in order to decrease the risk of transmitting SARS-CoV-2, the virus that causes COVID-19.

“Since COVID-19 can potentially result in asymptomatic or presymptomatic infections, individuals may exhibit no symptoms but still be able to transmit SARS-CoV-2 to other individuals. Because of that, it is important to take precautions such as COVID-19 testing before attending gatherings,” said Fred Turner, CEO and co-founder of Curative, a healthcare startup in the Los Angeles area providing testing and vaccinations for COVID-19.

“Many events are choosing to take preventative measures: ensuring all attendees are either vaccinated, recently recovered from infection, or have tested negative for COVID-19 before entering the space and mingling with other attendees,” he said.

Dr. Harrison Lobdell IV, MD, MPH, and a physician with TeamHealth in Austin, Texas, had a slightly different point of view and said the best times to use rapid antigen tests are when you are symptomatic. If you are exposed to someone with COVID-19 and test negative, he said you may want another test to fully verify your negative result.

“Rapid antigen tests should be used frequently in symptomatic individuals, but negative tests should always be confirmed [with a PCR],” he told Healthline.

How often should I test?

In the United Kingdom, for example, the National Health Service (NHS) recommends people do a rapid antigen test twice a week or every 3 to 4 days to check if they have COVID-19.

Their recommendation is based on data that indicates about 1 in 3 people with COVID-19 do not have symptoms.

Srinivasa Nagalla, MD, founder and CEO of commercial medical diagnostics company Diabetomics in Beaverton, Oregon, recommended people get both antigen and antibody tests once every 2 months, if they can.

“[Antigen tests are] most useful when you have symptoms between 9 and 14 days after exposure to COVID-19,” he said.

Should unvaccinated people approach testing differently?

As younger children remain unvaccinated, experts recommend they get tested periodically before going to school, sports’ practice, or a birthday party.

The rationale behind routine testing is that if the test misses a low-level infection one day, it is likely that it could detect a high-level infection the next time.

If unvaccinated people are planning on mixing with others who may be at higher risk of COVID-19, such as at a wedding or dinner party, doing a rapid test before the gathering can act as added precaution.

For people who are unvaccinated, Cioe-Peña recommended more frequent testing.

“[They] should get vaccinated if they are eligible. If they are not eligible, then they should just recognize that any contact with people is a high risk and they should test more frequently,” he said.

Meanwhile, Lobdell pointed out that vaccinated individuals who are exposed to COVID-19 are more likely to remain asymptomatic. In those instances where a vaccinated person is exposed to someone with COVID-19, he recommended trying to get a PCR tests over antigen tests.

He said unvaccinated people should be sure to quarantine if exposed to COVID-19.

“Unvaccinated individuals should quarantine for 7 days and be tested with RT-PCR if asymptomatic,” he said.

Most popular brands

Currently, there are many antigen tests available from makers such as Abbott, Quidel, Becton Dickinson, and others.

One of the most popular tests right now is BinaxNOW, made by Abbott Laboratories.

Abbott’s at-home antigen tests received emergency use approval (EUA) from the FDA at the end of August. The government ordered 150 million of the tests, which are roughly the size of a credit card.

The test costs about $24 over-the-counter in many drugstores in the United States.

Abbott said the company plans to increase production to 50 million per month in October.

Australia-based Ellume became the first company to get FDA approval to sell kits at major retailers such as Walmart, CVS, Target, and Amazon. However, the company recently issued a recall for 200,000 tests for showing false positives. Ellume said the recall did not affect most of the 3.5 million test kits shipped to the United States.

Some other popular options are Quidel’s QuickVue at-home test, Becton Dickinson and Company’s BD Veritor at-home test, and Access Bio’s CareStart.

The latest at-home test to get approval is ACON Laboratories’ Flowflex test. After being authorized on Oct. 4, the FDA said ACON plans to produce more than 100 million tests per month by the end of 2021.

This story originally appeared on: Healthline.com - Author:Yasemin Nicola Sakay