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So far, most patients being tested for COVID-19 get a nasal swab to see whether they’re positive or negative. But another testing tool is now making its way into doctor’s offices: serological tests, which examine the blood to detect antibodies created in response to COVID-19. Serological tests, sometimes called antibody tests, can help identify people who were infected with the coronavirus but either never developed symptoms or only developed mild symptoms without realizing what they were. This type of testing is important because it can help us get a clearer picture of how widespread the virus is — especially since asymptomatic cases of COVID-19 appear to be a lot more common than epidemiologists originally thought.
Manufacturers have been scrambling to make test kits that analyze blood taken from a vein, as well as a rapid finger-prick test kit. Coronavirus antibody tests are already being used in Asia. In the US, the FDA recently authorized the first coronavirus antibody test, which requires blood drawn from a vein. The status of the various tests that are currently in the works is rapidly evolving.
“It’s kind of like the wild wild West right now,” says Dr. Cheng Ruan, an internist at the Texas Center for Lifestyle Medicine. “This is all very new to the US. Everyone’s in a race to do it.”
Serological tests might also offer a lifeline to critically ill COVID-19 patients. In Texas, Houston Methodist Hospital became the first academic medical center in the country to transfuse donated blood plasma from a recovered COVID-19 patient to a critically ill one, hoping the antibodies will help them recover. In China, five critically ill coronavirus patients improved after receiving plasma transfusions.
Ruan’s office is among the first in the country to start testing patients’ blood for coronavirus antibodies. We asked him to explain the different types of tests that are currently being offered, what’s in development, how tests work, what they tell doctors and how long they take.
The primary test right now is a swab test. How does it work?
(Dr. Ruan) You’re looking for genetic material from the virus, or RNA. It entails putting a nasal swab in your nose all the way up to the sinuses. It’s not only uncomfortable, but you need a health care practitioner to do it right. It’s labor intensive. Plus, if you’re not forming enough mucus, you may not even be able to detect the RNA that’s in there, so you might have false negatives. That’s a downside. Results can take several days to come back. There’s one company coming out with an at-home swab, but it’s not available right now for the general public.
What does the blood test look at?
It’s different because it doesn’t test for the presence of the virus, but instead how your body responds to it from previous exposure. Serological tests look at immunoglobulins; they’re the bullets of our defense system. Within three to seven days of contracting this virus, your immune system will start to try to fight it off. It does that by producing antibodies against specific parts of the virus. One is IgM; it’s the largest antibody and the first to appear in response to toxins and viruses. As IgM continues to go up, our bodies then start producing another antibody, IgG. [It’s] like a heat-seeker missile against the virus. That too shows you were exposed to the virus and you’ve developed defenses against it.
Why should we test patients’ blood?
The benefit of testing immunoglobulins is that you can now stage where you are with the disease. If you have IgM against the virus — the first antibodies to develop — but not IgG, then we can assume you’ve had a recent exposure. It hasn’t been long enough for you to produce IgG. So then we can think about who you were in contact with recently and we can identify those people and start reaching out to them right away. I’ve already tested a few dozen patients and sent the samples to the lab for analysis. It’ll take about three to four days to hear back. The standard for this testing should be labs that have the most broad analysis of immunoglobulin toward different parts of the virus.
What can results tell us?
We’re probably going to find out more people have been exposed to the virus than we originally predicted, and that it’s been in the US a few months longer than we thought. One issue is that right now there are no official guidelines about what to do with results. I’m working with infectious disease, critical care and ER doctors around the world to try to come up with guidelines.
Another benefit might be that blood plasma could help critical COVID-19 patients. How does that work?
If a person tests with a high level of IgG, that means they’re actively producing heat-seeker missiles against the virus, and they can potentially save someone else’s life through a transfusion process. There could be a lot of people out there harboring life-saving immunoglobulins.
What about drawbacks to the blood test?
The downside of testing immunoglobulins is that people who assume they might be immune to the virus may not self-isolate. You might be immune toward one part of the virus, but it could mutate and you could pick up a mutated chain. So it still means stay at home. It doesn’t mean don’t wear masks and gloves. All it means is that you’ve been exposed in the past and you developed an immune reaction.
There’s also a finger-prick test in the works. How is that different?
That also tests for immunoglobulins, and results are much much faster, around 10 to 15 minutes. The whole idea is to abandon the blood draw, because it still requires people to come into a doctor’s office. A finger stick test could be ordered by a doctor and done at home, then follow-up could be done by telemedicine.
These tests will be readily available. We’re close to this. Everybody should get a finger-prick test. (One finger-prick test ordered by the UK works much like a home pregnancy test. Blood drops are added to a sample well, and lines appear that show a negative result, IgG detection or IgM detection.)
Patients haven’t been paying for nasal swabs. Is insurance also covering blood tests?
Insurance companies haven’t created a procedural code to cover them. That might change in the next few weeks though. That’s a big possibility.
You’re also working to set up a national monitoring program for high-risk patients. Tell us more about that.
Here in Houston, we recently set up stations in our parking lot to enroll Medicare patients in remote monitoring. We also enrolled people across the country. In total, a few hundred have signed up. We took their baseline oxygen reading, and then we have them self-monitor at home with a pulse oximeter, which measures heart rate and the level of oxygen going into your lungs. (Some patients with severe cases of COVID-19 develop serious respiratory infections and need supplemental oxygen.) Then we follow them. If we see anything abnormal, we reach out to them.
We’re the first ones to do this, and I’m trying to launch a national platform for doctors to monitor high-risk patients. I see this type of emergency prevention medicine continuing. COVID-19 is not a one-time thing. We know this isn’t the last time [something like] this is going to happen.
This interview has been condensed and lightly edited.