Much has changed about testing for current COVID-19 infection and antibody testing for past exposure. Here’s an updated guide on what you need to know:
Diagnosing the virus
What we have now: The most widespread tests to diagnose current COVID-19 infection are the polymerase chain reaction — or PCR — tests that involve swabbing a person’s nasal passages and looking for the coronavirus’ genetic material.
Results come as quickly as less than 15 minutes with the rapid test, about which false results have been an issue, or within a couple of days if sent to a lab.
What’s coming: More tests are on the way. Scientists at Sherlock Biosciences in Cambridge, Massachussetts, are using gene-editing technology known as CRISPR to develop another type of rapid test that could be produced for as little as $6 per test.
And a new saliva test developed at Rutgers University holds great promise because it would be easy to administer even at home.
“Anybody can spit,” says Dr. Robert Murphy, executive director of the Institute for Global Health at Northwestern University’s Feinberg School of Medicine, who is helping a national effort to develop point-of-care technologies. “Saliva will open the door for mass testing.”
What about antigen tests: Think rapid-strep tests. These still involve a swab like the PCR tests, but give quicker results and are cheaper and simpler to manufacture.
Antigen tests target substances given off by a virus that trigger antibodies in an infected person.
These drew widespread attention recently when Quidel Corp. of San Diego got federal approval for its rapid COVID-19 antigen test. But don’t expect to be able to get one yet. Quidel has said it’s aiming to produce 1.8 million of the tests a week by this summer.
The antigen tests will be relatively easy to manufacture and use. But they produce a higher number of false-negative results.
Still, they could be useful if combined with PCR tests or used in a testing program in which people — say, at a nursing home or factory — get retested often.
Confirming past infection
How they work: We now know these as antibody tests. They involve a blood test — yes, stick out your arm, and make a fist — but a briefer one than you might be used to.
They test a small amount of blood for the presence of antibodies produced by the body’s immune system.
With COVID-19, these antibodies usually appear 14 to 21 days after infection. So these tests are done after the fact, as confirmation.
What they might reveal: Beyond that, there’s hope that having the antibodies might protect against future infections.
One problem: Many of the antibody tests that were rushed out, with no vetting by the government, in response to the pandemic aren’t very accurate.
Also, scientists don’t know how long antibodies stay in a recovered person’s system or how well they might protect us. Antibodies to the onetime scourge of measles, for instance, protect a person forever. But antibodies to the common cold or influenza — not so much because of the wide range of cold and flu viruses and those viruses’ ability to rapidly mutate.
Still, scientists are eager to launch widespread antibody testing to get a big-picture look at where the virus has hit — within geographic areas and among certain populations.
What else is coming
For weeks, Chicago and the state of Illinois faced a shortage of test kits and swabs.
Now, we’ve reached the point where anyone who feels ill can and should be tested for COVID-19, says Dr. Emily Landon, executive medical director for infection prevention and control at University of Chicago Medicine: “We’re currently at a place where anyone who has symptoms can be tested.”
The same is true if you suspect that you’ve been exposed, symptoms or not, Landon says.
Though some places are charging for these, many hospitals and clinics are offering no-fee tests.