I wanted to know if I could safely visit my mother and give her a hug, so I let strangers stick needles in my arm.
Unfortunately, both of those blood tests for novel-coronavirus antibodies came out negative, meaning I remain vulnerable to being infected and infecting others. (Sorry, Mom.) But at least I learned something about how this testing works and what it can reveal.
Antibody tests, also called serological tests, differ from the diagnostic tests that check for the virus’s genetic material. Instead of showing where the virus is today, they reveal where it’s been, as seen in the virus-fighting antibodies that your body develops two weeks or so after a novel-coronavirus infection.
These tests also feature a less invasive patient experience. Instead of having a swab inserted uncomfortably far up your nose, you sit through a quick blood draw from a vein in your arm.
But for months, serological tests were as hard to schedule as the first diagnostic tests. It didn’t help when companies rushed to ship inaccurate tests after the Food and Drug Administration eased its usual approval process to try to cope with the coronavirus crisis.
The FDA has since revoked many of those temporary authorizations, while reliable antibody tests have become available through more channels—including some that don’t need an in-person doctor’s appointment to authorize the test.
Two that I tried only required a mobile app: PlushCare, a $15/month telemedicine service, and Forward, a small chain of high-tech doctors’ offices that charges $99/month (normally $149/month) for comprehensive care. (The firms comped those service fees, while my insurance covered all but a few dollars of the test costs.)
With PlushCare, I had to complete a basic health profile in that San Francisco firm’s iOS app (it was fine with my not knowing my current blood pressure or heart rate). Then I picked a doctor from a list of those available on a given day.
My remote consult came in a video call through the app. The doctor—an American who had retired to France before signing up with PlushCare—quizzed me about COVID-19 symptoms I might have experienced.
Kate Grabowski, Johns Hopkins School of Medicine
The lower the prevalence of the disease in the population, the lower the likelihood that your testing positive means you had the disease.”
The doc said he’d put in for the test, adding “let’s hope it’s positive.” Minutes later, PlushCare sent an e-mail with a test-order PDF to print and take to the nearest Quest Diagnostics location.
Quest’s site stalled out while I was trying to book an appointment, but I only had to wait a few minutes as a walk-in patient. A few minutes and a small test tube’s worth of blood later, I was done.
With Forward, I used the messaging system in the San Francisco-based company’s Android app to request a test, citing that February cold as my reason. Two days later, I had an appointment booked at Forward’s downtown-Washington D.C. location.
That visit doubled as a chance to update my vitals; it appears that being cut off from the conference lifestyle let me drop several pounds. The blood draw was as quick as at Quest.
Both tests yielded an answer in under 24 hours: negative. So that cold and all the crowded events I’d attended as late as March 9 have not given me any immunity.
On the upside, I didn’t have one test show positive and another negative. That’s a real scenario, and in that case I would have had to try a third online test-procurement option such as those available through the sites of LabCorp and Quest.
(Quest’s service requires a $119 testing fee upfront that you can then try to get reimbursed by your insurance.)
Not 100% reliable
Why would different tests yield different results? “There’s variability in the quality of these tests,” said Kate Grabowski, an assistant professor of pathology at the Johns Hopkins School of Medicine in Baltimore. Their accuracy still isn’t high enough to let you take a single positive test to the bank—so although you can now get an antibody test for free by donating blood, that should not be your reason to give blood.
Epidemiologists call that problem if iffy positive results “low sensitivity.” Forward’s site estimates that 90% of its positives results are accurate,, compared to 99% specificity, or correct negative results. And the issue increases in places less besieged by COVID-19.
“The lower the prevalence of the disease in the population, the lower the likelihood that your testing positive means you actually had the disease,” says Grabowski. For example, a positive test in mostly-untouched Vermont isn’t as likely to confirm actual exposure as one in COVID 19-wracked New York City.
Grabowski adds that sequential tests yielding the same result should be deemed more reliable (though even then, they may suggest a confirmed infection never happened). But they still can’t answer unsolved questions remain about the protection conferred by surviving this disease.
“We think that [antibodies are] protective,” she says. “We’re not really sure how long these antibodies last.”
Upcoming advances in testing such as at-home kits that would let you take a pinprick of blood and drop it on a reactive surface can’t help with that larger picture either, although more widespread testing such as the nationwide tracking now underway from the Centers for Disease Control can help define the extent of the problem.
In other words: Yes, you should still wear a mask.