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The Way States Count Test Results Matters As Antigen Testing Comes Online In Mountain West

Antigen tests look for proteins on the surface of the virus that causes COVID-19. While other tests including PCR require laboratory work to process, some antigen tests can yield on the spot in minutes, much like a pregnancy test.

Antigen testing is expected to become a more common way to test for COVID-19. It looks for the virus’ surface coating, rather than pieces of its genetic material. It’s faster and easier to administer than other tests.

But, as Kaiser Health News has reported, Mountain West states differ in how they handle the results, representing three of the approximately 20 states that were lagging when it came to collecting the results of antigen tests. However, over the past few weeks, the states have broadened the scope of the test results they collect.

Reporting antigen test results is critical, experts say, because they can help quickly detect the shifting scale of an outbreak.

“We need complete and accurate data to make informed policy decision making,” said Bailey Fosdick, a statistician with Colorado State University who is currently working on studies of COVID-19 prevalence.

Colorado now requires providers to report the result of all COVID-19 antigen tests, both positive and negative. Wyoming receives some positive antigen test results. And Montana requires positive results to be reported. Spokespeople with the Wyoming and Montana state health departments said antigen testing has only recently begun in their states, and that the vast majority of COVID-19 testing continues to be PCR.

Fosdick said antigen tests are more likely to give false negatives, occasionally designating someone “negative” when in fact they had the virus on board. Still, with this pandemic, the more data the better.

“We want to have that data for understanding what’s going on today: ‘What is the current state of the epidemic?’” she said. “But we also want this data so that months — years — from now, we can look back and say ‘What was going on? How did our policies affect transmission of the virus in our area?’”

And, she pointed out, if antigen testing continues to grow in popularity in coming months, states will need to collect both positive and negative results in order to calculate test positivity, an indicator often used to determine how widespread an infection is (and sometimes whether a state is testing enough, too).

Sue VandeWoude, a virologist also working on coronavirus surveillance with Colorado State University, said antigen tests might not be as good at detecting every positive, but there’s some evidence they may be better at indicating if someone is actually contagious.

“So there’s a balance I think with the antigen test, that while they may miss infections much more commonly than PCR, the hope is that they would actually detect infections that matter more in terms of transmitting the virus to other people,” said VandeWoude.

As researchers at Harvard and the University of Colorado Boulder wrote in a draft article earlier this month, it’s more important to be able to test for COVID-19 frequently than it is to use a test that doesn’t miss a single positive.

“From that perspective, this is really the future in how we can hopefully begin to open up safely because we’ll have a better pulse on what’s going on,” said statistician Bailey Fosdick. “And it’s OK if a few of those infections get through the cracks as long as we’re catching the large majority of them.”

This story was produced by the Mountain West News Bureau, a collaboration between Wyoming Public Media, Boise State Public Radio in Idaho, KUNR in Nevada, the O'Connor Center for the Rocky Mountain West in Montana, KUNC in Colorado, KUNM in New Mexico, with support from affiliate stations across the region. Funding for the Mountain West News Bureau is provided in part by the Corporation for Public Broadcasting.

Rae Ellen Bichell was a reporter for KUNC and the Mountain West News Bureau from 2018 to 2020.