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How a home COVID test works and when to use it

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Health officials are increasingly emphasizing the importance of rapid at-home testing as a way to help slow the spread of the COVID-19, especially with the delta variant, which is driving new cases, and omicron, which has emerged as a potential threat.

These over-the-counter tests, which first appeared in pharmacies in spring 2021, require a quick swab of the nose and provide results in about 15 minutes. And soon its price could drop from about $20 a box to zero, as the federal government (in English) order health centers to offer them free, and that insurance companies reimburse the cost of the kits that have been purchased.

How reliable are these tests? And when should you consider taking one? Top experts answer common questions and offer helpful tips for doing a COVID test at home.

How do rapid at-home tests work?

Like many COVID tests administered in doctors' offices and testing centers, an at-home version can determine if you are infected with the coronavirus, through a swab taken from your nose. These tests, called antigen tests, work by looking for the presence of specific proteins associated with the coronavirus. If detected, a positive result appears on a test strip within minutes, like a home pregnancy test.

“And that's helpful because it allows you to make individualized decisions about how far you should stay from other people, what medical care to receive, and how to stop cycles of transmission with your behavior,” Dr. Cameron Wolfe, a specialist in HIV, explained at a recent briefing. Infectious Diseases at Duke Health and adjunct professor at Duke University School of Medicine.

When should you take a test at home?

Even if you're fully vaccinated, it makes sense to get tested at home if you have COVID-19 symptoms or have been exposed to the disease, they say the Centers for Disease Control and Prevention (CDC). It's also recommended that you get swabbed before gathering with others indoors, whether that's dining with a small group of friends, a festive gathering with family or a large event, such as a concert.

“The way I would recommend using rapid antigen tests is really as a screening method,” Stephen Kissler, a researcher in the Department of Immunology and Infectious Diseases at the Harvard TH Chan School of Public Health, told reporters Dec. 7.

You may have to wait several days for results from standard PCR (polymerase chain reaction) tests administered at many doctor's offices and testing centers. “And by the time you get the results, they're often not very meaningful,” Kissler says, because you may have been infected during the waiting period.

However, a rapid test performed from the convenience of home provides “immediate and practical results,” says Gigi Gronvall, a senior scholar at the Johns Hopkins Center for Health Security and an adjunct professor at the Johns Hopkins Bloomberg School of Public Health. “If your result is positive, don't get close to other people, because you have infectious virus in your nose. Therefore, it is a good public health tool to ensure that people who are potentially contagious keep their distance.”

The key is to get tested as close to your plans as possible; Try to do it the same day, Matthew Binnicker, director of clinical virology at Mayo Clinic, explained at a recent briefing. “That will give you the best information [about] whether someone has high amounts of the virus in their system at that time.”

Types of COVID-19 tests

PCR test: a type of molecular test that looks for active coronavirus infection by detecting genetic material from the virus. A sample is usually obtained with a nose swab, although a throat swab or saliva sample is also useful. You can have these tests at your doctor's office or at a testing center. Because these tests are analyzed in a laboratory, it may take a day or longer to receive results. These tests are considered the most accurate available.

Quick test: Also known as an antigen test, this type of test looks for pieces of coronavirus protein, usually through a nasal swab. Rapid tests — which can be administered in a doctor's office, pharmacy, or at home — offer much faster results (about 15 minutes) than PCR tests because they do not need to be analyzed in a laboratory. The tests are considered accurate when there is a large amount of virus in the body, but they can miss early infection.

Antibody test: This type of test can help determine if you have already had COVID-19; does not identify a current infection. Using a blood sample, the test looks for antibodies produced by the immune system to fight an infection. Are you fully vaccinated? You should know that the COVID-19 vaccine can cause a positive antibody test result for some antibody tests, but not all, the FDA says. 

Source: Yale Medicine/FDA


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Yair Ramirez
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