What you need to know about rapid tests vs. PCR tests for COVID-19

The point-of-care tests are a fast and cheap, though less accurate, way of detecting the virus compared to sending nasal swabs to a lab.
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Posted at 11:46 AM, Aug 07, 2020
and last updated 2020-08-07 11:46:21-04

The rapid type of coronavirus test that Gov. Mike DeWine took on the tarmac before greeting President Donald Trump could be more widely available in Ohio if the state succeeds with a group purchasing agreement with six other states for these types of tests.

Gov. Mike DeWine announced Wednesday the state’s plan to enter a multi-state purchasing agreement with Maryland, Louisiana, Massachusetts, Michigan, and Virginia to expand the use of rapid point-of-care tests.

These tests use a different method of detection that is faster and cheaper, though less accurate, than the more common method of coronavirus testing, which is a PCR test, where a nasal swab is sent to a laboratory.

DeWine said at his Wednesday press conference that the states are joining together to ramp up the use of this type of test in order to “detect outbreaks sooner with faster turnaround time; expand testing in congregate settings such as nursing homes and assisted living facilities; and make testing more accessible for the most high-risk and hard-hit communities.”

Testing serves several purposes in responding to the pandemic. It can provide a diagnosis for a person who might need care. It lets people know if they are infectious so they isolate before spreading the virus any further and so their close contacts can be aware they were exposed and thus could also be sick. It also adds to the data available on how and where the novel coronavirus is spreading, so public health officials can adapt measures as needed.

For the past week, Ohio Department of Health has reported there have been an average of 22,000 tests performed in Ohio a day, more than double where the state was six weeks ago. There are however can be lags in getting lab results in a timely manner as demand surges. In addition, some groups such as nursing homes have struggled to get the quick, cheap and routine testing they’ve long requested, given the impracticality of a nursing home relying on drive-thru testing.

These rapid tests are now on the market and have gotten more accurate than in the beginning of the pandemic but test makers haven’t aggressively ramped up manufacturing. DeWine said the group purchasing plan demonstrates to testing manufacturers that there’s a significant demand for this type of tests, and the pooled agreement also has the potential to help states buy these tests in a cost effective way.

Rapid antigen tests vs. PCR tests
If you’ve gotten a coronavirus test — such as at a drive-thru or pop-up site — you likely received a PCR test, which involved someone taking a sample from your nose with a swab and sending it to a lab.

PCR (polymerase chain reaction tests) are highly accurate tests that work by extracting and amplifying genetic material from the novel coronavirus, according to Peter Mohler, chief scientific officer for the Ohio State University Wexner Medical Center.

They are much more sensitive than a rapid test, meaning PCR tests can pick up very tiny amounts of virus so they have a high likelihood of catching an infection and not giving a false negative.

These tests are a more expensive option, they take a more complex supply chain and take more human labor as well as laboratory capacity to complete — all of which are in high demand right now as everywhere in the U.S. tries to run more tests.

Rapid tests like the one DeWine used are what are called antigen tests.

“They can be done similar to how you would do a flu tests or a strep test,” Mohler said. “You can imagine having these in a doctor’s office or even a nursing home and to be able to test whether someone has it in, say, 15 or 20 minutes. The disadvantage is that they’re just not as sensitive as that molecular PCR test that we’ve been hearing about over the last few months.”

Both antigen tests and PCR tests have a place in the toolbox when it comes to responding to the pandemic, Mohler said.

This method of testing is nearly immediate, which lets contact tracing start sooner with a virus where time is of the essence. When there’s a positive test result received quickly, it raises the likelihood that an infectious person can be isolated before they get a lot of other people sick.

The accuracy of available antigen tests have improved since the start of the pandemic but they still aren’t as accurate as PCR tests. A positive antigen test for the coronavirus is pretty trustworthy but a negative test needs treated with more caution because the person might actually still be infectious.

“The point-of-care tests that we have available right now for COVID still suffer from some sensitivity issues,” said Dr. Roberto Colón, vice president of quality and safety for Premier Health. “And that means that when they have a negative test, if you still have concerns for COVID or if it was still a patient that you suspected you may have COVID, you may need to either repeat the test again or have another test to actually confirm that it indeed was negative. ”

Colón said the timing of antigen tests in the disease course is important. Later in the disease, people shed less antigen and someone with symptoms as little as seven days could have a false negative.

“That’s not something we typically see with viral PCR. That’s something that’s very different between those two tests that has to be taken into consideration when we look at the strategy,” Colón said.

“The best place to use these antigen tests is large groups of population screening,” he said, where these tests can be quickly deployed and then health officials can figure out which patients in the group need a secondary screening.

Finalizing deal

With the plan to get more of these tests to Ohio, the bipartisan group of three Republican and four Democrats are talking with test makers Becton Dickinson and Quidel to purchase 500,000 tests per state or a total 3.5 million tests.

Several steps that would have to pass for the plan to translate to tests on the ground in Ohio. What the governors did was sign a non-binding agreement and would need to hammer out a final contract with all the relevant parties before testing machines and related supplies were ordered. More states could sign onto the plan.

The Rockefeller Foundation is guiding the testing strategy and offering credit if needed to finance the plan.

The Journal-News is a partner of WCPO.