COVID-19 testing best during small window of time
With months of the COVID-19 scare has come a need for reassurance for some; sometimes just knowing if you've got it — or had it — is enough to dispel at least some of the fear.
SSM Health St. Anthony Hospital-Shawnee Dr. Gregory Grant said the timing that goes with testing is playing a large role in how test results are coming out.
He said there are three types of tests that are being used in all sorts of areas — there's the RTPCR (or PCR), antigen testing and antibody testing. The first two are nasal swabs used to determine if someone is currently sick with COVID-19. The antibody test is used to see if a person has had the disease at some point, though good timing of the test is vital — and even then only three-fourths of documented positive cases are showing confirmation through the blood test.
RTPCR (or PCR)
The PCR is the most common and most accurate, Grant said; it's a much deeper swab than is typical for tests most residents are used to, like the flu or strep.
Called a nasopharyngeal swab, it goes in a bit farther than just the tip of the nose.
“That's in order to get a better test result,” Grant said.
The PCR swab goes in through your nostril, through your sinuses, to the back of your throat.
It is recommended to do both sides (nostrils).
“We can probably get a good test from just one side,” he said, “but they try and do both sides to make sure.”
Grant encourages people to go through both sides because that does give a better chance of getting a good result,
“But I know that some people have a really violent reaction to that first swab,” he said. “I've been swabbed twice myself, and, yeah, it's not comfortable.”
The PCR test is used to get copies of the virus.
“They immediately capture that to a transfer medium, which helps preserve the virus,” Grant said. “Then they take that to the center where it's going to be tested and they take that sample and they amplify it many times over, and if there's even one virus particle that's in there, that should be amplified enough times where they can see if it's a positive result.”
He said the minimum turnaround time — if you have access to be able to put your sample directly on the machine — is 24 hours.
“In reality, of course, we have to get all the tests together and then send them in, so typically 48 hours is what we were seeing when we were getting these results several weeks ago,” he said. “A few weeks ago, there were so many people being tested that there was kind of a bottleneck in the testing.”
He said some people were getting results within 48 hours, for a lot of people it was 72, and sometimes it has been even as long as seven days.
“The test itself takes about 24 hours to run, but there's a little bit of a bottleneck in the capability of the machines to do the testing,” he said.
Grant said the most data being used is coming from the PCR test results.
Antigen testing is done using a shallower swab, the kind of testing that would normally be done like a rapid flu swab or strep swab.
“We don't do antigen testing at SSM,” Grant said. “I know some places around the state are using that.”
He said, not only is the swab less invasive, but the test is different, as well.
“It's not going to be as accurate because it's not able to amplify the virus,” he said. “It just has to go off of certain proteins that you can target for this particular virus.”
So if a resident is asymptomatic, the antigen testing is that's just not going to be a good test, Grant said, because with absolutely no symptoms, the antigen test is more likely to be a false positive than a true positive.
“That's the real downside to the antigen testing,” he said. “The good side is that you get the results back in 15 minutes to three hours like that, depending on which one you're using.”
For those with symptoms, tests seem to show positive a little bit later in the course, he said.
Once a person first starts getting symptoms, the antigen test is probably going to show positive two to three days after symptoms begin.
“That's when you have the best chance of that being an accurate test result,” he said.
The antibody testing — a blood test, is not going to be testing for current infection.
“It's an IGG antibody, and those typically show up two to three weeks after you've had the virus,” Grant said. But interestingly enough, he said only about 75 percent of the people that had documented positive PCR testing are showing up positive on the IGG — so 25 percent of people are not even making the IGG antibody, he said.
“So, if it's positive, that helps you a little bit,” he said, “but if it's negative you could have still had it sometime earlier in the year like some people feel like they might have.”
He said health officials don't know how long those antibodies last.
“They may only last 90 days, so if you're someone thinking you had this early on when the disease was being transmitted back to March, it's possible by now those antibodies have faded,” he said.
For most people who get COVID-19, Grant said the PCR test is probably only going to show positive in that first 10 days of the infection.
He said the downside to the PCR testing is that it's possible to not show a test-positive if a person was tested a little bit too early in the course — or too late.
“You're actually contagious they think two days before your symptoms start,” he said. “People are no longer contagious after 10 days, which is why the CDC has those guidelines that if you're asymptomatic at the 10-day mark, and it's been at least three days since your last symptoms, it's okay to return to work without being tested again,” he said.
Grant said, early on those who were asymptomatic were encouraged to get tested, so health officials could get a handle on the numbers for more data.
But now there's a shift away from that, he said, trying to focus on those who are at higher risk for exposure and symptomatic people.
“For asymptomatic people who have a high risk of exposure, I think it's probably a good idea to get tested,” he said, “but we're trying to lean toward focusing resources on those who are symptomatic.”
He said he doesn't want to discourage anybody from getting tested if they feel like they've had a high risk of exposure to somebody.
At this point, Oklahomans are running the risk of COVID fatigue, Grant said and they need to step up the vigilance right now.
“The State Department of Health put together a nice way of tracking this (COVID-19 Alert System) statewide on a weekly basis,” he said. “They've got a color-coded at-risk map where they show the number of new infections on average per week, per county.” Pottawatomie County is still in yellow, the low-risk category.
He said a recent upward trend looks like more disease activity is going on, because the percentage in the number of positive tests are going up.
“Even though we're doing more testing, the percentage of positive tests are actually higher, also, which tends to go along with the idea that there's actually more disease activity,” he said. “If we were getting a whole bunch of tests and actually the percentage of those positive tests were going down, that would indicate that our numbers are going up because we are doing more testing.”
By the numbers
According to cdc.gov, as of July 30, there were a total of 52,942,145 COVID-19 tests reported so far in the U.S. Of those, 5,046,506 (or 10 percent) were reported as positive. Total deaths (in the U.S.) related to COVID-19 so far have been reported at 150,283.
Did you know?
Two kinds of tests are available for COVID-19: viral tests and antibody tests.
A viral test tells you if you have a current infection.
An antibody test might tell you if you had a past infection. An antibody test might not show if you have a current infection because it can take 1–3 weeks after infection for your body to make antibodies. Having antibodies to the virus that causes COVID-19 might provide protection from getting infected with the virus again. If it does, the CDC states it does not know how much protection the antibodies might provide or how long this protection might last.
Information gathered from the Centers for Disease Control and Prevention, at cdc.gov.