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Are antigen tests the silver bullet to Pa.’s coronavirus testing delays? Not so fast.

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The PCR test, shown here, is the current gold-standard for detecting active coronavirus infections. Pennsylvania wants to expand the use of another, less precise test — known as an antigen test — to combat delays in getting test results.
TIM TAI / Philadelphia Inquirer

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“Do I have COVID-19?”

In Pennsylvania and across the country, coronavirus test results are sometimes taking weeks to come back. Those delays are frustrating for those who might be sick, and just plain unacceptable to state officials.

“Two weeks, that’s almost useless,” Gov. Tom Wolf said recently.

There’s a promising solution, state officials announced Aug. 11, and it’s coupled with an economic boon. A company in the Lehigh Valley, OraSure Technologies, is expanding its operations and working to develop two kinds of rapid COVID-19 tests.

But there’s a catch.

Neither antibody tests nor antigen tests — the two kinds OraSure is developing — are the gold standard for determining if a person actively has COVID-19.

Antibody tests search for past infections, which may be helpful as people need to wager how much risk they are willing to take in getting together with loved ones or returning to school or to work. But antibody tests cannot provide insight into whether people currently have the coronavirus.

Antigen tests, on the other hand, are starting to make some waves. Like PCR tests — the most common and reliable type of COVID-19 test — antigen tests look for active infections, but they don’t have the same sensitivity levels as PCR tests. Put another way, they can’t detect COVID-19 as well.

At a news conference Aug. 6, Health Secretary Rachel Levine warned Pennsylvanians that antibody and antigen tests might not be useful in every situation.

Regarding antigen tests specifically, Levine said the state health department has heard that the federal Centers for Medicare and Medicaid Services plans to send antigen test kits to Pennsylvania nursing homes, which she said is “going to be a challenge.”

”What we’re concerned about is the sensitivity and the specificity of those tests, meaning the false negative rate and the false positive rate,” Levine said.

According to the health department, positive antigen tests are only included in the state’s COVID-19 count as probable cases, not confirmed cases, and all data-driven decisions about reopening rely on confirmed numbers from PCR tests.

The state’s negative count, a department spokesperson said, only includes negative PCR test results.

So, though the expansion of rapid testing in Pennsylvania is an exciting development and will certainly help to identify people likely to spread the virus, it might not be the silver bullet Pennsylvanians are hoping for.

For quick reference:

» PCR tests: The gold standard in COVID-19 testing. PCR tests are widely regarded as the most reliable tests, but turnaround times can lag.

» Antigen tests: The “rapid” tests that are starting to become more available across the country. Antigen tests are easy to administer and quick to turn around, but they aren’t as sensitive as PCR tests, meaning they might not be able to detect low levels of the virus, potentially leading to a high rate of false negatives.

» Antibody tests: Potentially useful in determining whether you may have already had COVID-19, though scientists warn there is still a lot we don’t know about what testing positive — or negative — for antibodies might mean.

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Sara Simon

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