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How COVID-19 testing works and why Minnesota’s capacity to do it is limited

Even with more testing supplies, lab capacity is limited.

Medical personnel swabbing an employee’s nose
Medical personnel swabbing an employee’s nose at a drive-through testing site for coronavirus for employees at UW Medical Center Northwest in Seattle, Washington.
REUTERS/Brian Snyder

There have been a lot of questions about testing for COVID-19 in the ten days since Minnesota got its first confirmed case of the virus.

The biggest one is why there aren’t more tests available. The Centers for Disease Control has been under fire for not ramping up the distribution of tests to state and local health departments, forcing front line workers to ration them.

But even with a bigger supply of test materials, labs’ capacity to do the tests once they receive them is also a limiting factor: in Minnesota, only the state Department of Health’s lab could test in the first few days of the outbreak in the state. Now, the Mayo Clinic and several commercial labs are processing kits to help, too.

Here’s how the testing process works.

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Who should get tested

As of Saturday, the Minnesota Department of Health was recommending people who meet certain criteria, like having traveled somewhere with a high number of COVID-19 cases or having exposure to a confirmed case, be prioritized. But the department said Saturday it was giving health care providers some discretion in who to test and not test.

Symptoms of COVID-19 include fever, cough and shortness of breath, which are likely to develop between 2 and 14 days after exposure to the virus, according to the CDC. MDH is not currently recommending people who are not displaying symptoms of COVID-19 be tested, and has asked medical providers to test for other respiratory illnesses, like flu, before testing for COVID-19.

For those wondering if they need a test, it’s best to call your medical provider to get a testing referral — visiting a health care setting with potential COVID-19 symptoms can expose others to the virus.

Getting swabbed

Once you have a referral, you can use a drive-up or other testing site. M Health Fairview, the Mayo Clinic and other facilities are offering this service.

In most places, medical professionals collect two swabs, one called a nasopharyngeal swab, which goes through the nose and into the pharynx, and another, a throat swab, said Dr. Mark Schleiss, a professor of pediatrics in the University of Minnesota Medical School.

Those samples get sent to a lab, where it goes through a process called detect reverse transcriptase PCR (the PCR stands for polymerase chain reaction).

“[It’s a] test that’s specifically looking to detect the RNA of the coronavirus, basically the genes of the virus,” said Louis Mansky, the director of the Institute for Molecular Virology at the University of Minnesota.

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In the lab

The lab worker puts the sample in a solution and extracts all its RNA.This likely includes RNA from cells from the person’s nose and throat as well as any virus RNA present.

Then comes reverse transcription, which basically involves making a DNA copy from the RNA.

Since scientists very quickly sequenced the coronavirus’ RNA, they know what to look for. They use a device called a thermocycler, which, among other things, changes temperatures to amplify the target that represents a part of the coronavirus’ RNA, Mansky said.

Lab workers use things called fluors — little tags put on DNA and RNA molecules — to detect the virus, Schleiss said.

“If you get them excited, they will glow … it will release the fluors, as the abbreviation implies, it is a fluorescent signal, and the machine can read that,” he said. That signals a positive case of COVID-19 .

Though more commercial labs are becoming available to run tests in Minnesota, lab capacity is limited.

“Even with more laboratories [available], the challenge is that all those laboratories are needing to use the same elemental components for their tests, so that puts pressure on the entire system within Minnesota, within the country, across the globe,” said MDH Infectious Disease Director Kris Ehresmann said in a weekend press call. So that becomes the challenge, making sure that everyone still has the necessary components they need to be able to test.”

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In some cases, COVID-19 test results are being turned around in 24 hours. An MPR producer who was tested in Minnesota last week said she learned of her negative result within two days.