DETROIT – President Joe Biden’s administration is making a push to get the coronavirus pandemic under control by improving vaccination levels and by creating a new provision to make at-home COVID testing more accessible.
Local 4′s Dr. Frank McGeorge explains what the at-home rapid tests are, how they work, and when you should use them:
Thanks to COVID, everyone’s had a crash course on immunology, but it can still be confusing. Generally, there are three different tests for COVID.
The first is blood antibody tests that look for your immune response to having already been infected. Next are PCR or “molecular” tests that look for the genetic material of any virus present. These are considered the gold standard, but the results take time. Finally, there are the tests we’re focused on here, called rapid antigen tests, or simply rapid tests.
How rapid antigen tests work
Rapid antigen tests use a nasal swab to collect a sample from the nose, just like the fancier PCR tests, but these are looking for something completely different.
Rapid tests look for actual pieces of the virus, specifically, something called the “nucleocapsid protein,” which is also referred to as an “antigen.” That’s why rapid tests are also called antigen tests.
This nucleocapsid protein is different from the well-known spike protein, but it is just as important for the function of the virus. If any of this nucleocapsid protein is found by the test, it can be marked, most often by a line appearing in the results area.
7 rapid tests have authorization
There are currently seven rapid tests that have authorization for use as a home test. While the underlying technique of marking the antigen is the same, they each have different steps that need to be followed before you get a result. While some have results that can easily be read by the patient, like a home pregnancy test would be, others require a smartphone and some fancy gadgetry to interpret the result. The results of these tests are available generally in about 15 minutes.
It is important to understand, these rapid tests are not perfect. Because they measure actual amounts of virus protein, they become more sensitive when there is more virus present. At the start of an infection, before there is a lot of virus, they may be falsely negative. If the test is repeated in a couple of days, when there is more virus, it is more likely to turn positive. That’s called serial testing and it’s the recommended strategy to monitor someone after an exposure. That way you can pick it up as soon as it’s detectable and decrease quarantine time.
Another good use for rapid tests is screening before an event, like a party for example. The important thing in that situation is, when you are testing people that don’t have symptoms or a known exposure, the test is less sensitive because an asymptomatic person, even if they have COVID, isn’t likely to be shedding as much virus. The good news is that they are also less likely to be highly contagious because they are shedding less virus.
How accurate are home rapid tests?
Home rapid tests aren’t as accurate as PCR testing done in a lab. But, while we might strive for the highest accuracy of the PCR test, what good does it do if the results take 24 hours or more to return. By that time, if a person is positive, they’ve potentially already exposed their close contacts. Rapid tests allow for easy less expensive repeat tests at the time a result is most relevant. In a situation where someone was directly exposed to COVID or has symptoms that could be COVID, serial negative rapid tests can be used to keep a person out of quarantine while the more sensitive PCR results are being completed.
Finally, I should mention, these tests aren’t free. Even with the federal government partially subsidizing the cost they’ll probably still be between 5 and 15 dollars each. This will leave many people to decide whether frequent repeat testing, which is the goal, is worth the personal cost.