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Rapid Antigen testing effective, comes with some caveats

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Antigen Test Card

MADISON (WKOW) -- As the coronavirus spreads throughout Wisconsin, so does the need for testing.

One test could get you results in as little as 15 minutes, and it's only going to become more widespread.

Wisconsin is expanding access to rapid antigen testing at several UW system schools.

The rapid test eliminates the multiple-day waiting period you'd experience with a typical PCR test, but there are concerns over its accuracy.

On Thursday, UW-Madison began offering community antigen testing at Nielsen Tennis Stadium.

On Monday, staff said it was the busiest day so far.

Megan Kinney was one of the people getting tested, and was shocked by how fast she got her results.

"You have the option to either get them emailed to you, or sit and wait 15 minutes to get the results and actually the email came through and gave me my results," she said.

The speed comes from not having to send samples to a lab.

A chemical reaction happens on a card similar to how a pregnancy test works.

Doctor Jeff Pothof with UW Health says the test is very effective in certain circumstances.

"If you get an antigen test and it's positive and you have symptoms the likelihood of you being a true positive very, very high," he said.

If you have symptoms and you get a negative result, he says act as if it was positive and wait until you can get a follow-up PCR test.

The antigen test is also not very precise for asymptomatic people.

"If you're asymptomatic and you get a positive, that would give me pause, that probably means that you should act as if you're positive until that confirmatory test comes back," Dr. Pothof said.

The difference comes from how the tests work.

The "gold standard" PCR test takes a sample, looks for any trace of the virus, and causes it to multiply to know for sure that someone has the virus in their system.

The antigen has to have large enough quantities of the virus already present for the chemical reaction to happen.

Because this isn't a foolproof test for accurate results especially if you're asymptomatic, follow-up testing is crucial.

However, Dr. Pothof says it helps lessen the strain on resources on the more precise PCR tests.

"[The PCR test] requires a lot of reagents, it requires a lot of lab wear, plastic, pipettes, it requiers a lot of large expensive machines that you can't just plop down into any CVS or Walgreens," he said. "The antigen test is really cheap, you can set it up anywhere."

Dr. Pothof says the best way to get around the test's downsides and still use it as a screening tool, is to test people daily. That's why the test is used to make sure NFL players are clear for play.

"Obviously you're not going to be able to test the population of Madison, half a million people in the general area, every day for Covid 19," he said. "There's just no possible way to do that."

UW Health is studying to see if they can use antigen testing to check if hospital staff are safe and able to work on a daily basis.

UW Madison has 80,000 antigen tests to administer until the end of the year.

You have to make an appointment ahead of time to get tested.