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There are several reasons our concierge primary care doctors at MD 2.0 in Jupiter are often asked whether rapid at-home COVID-19 tests are are good idea.

• The SARS-CoV-2 coronavirus is so contagious.
• Only about 54 percent of Americans have been vaccinated against it.
• Many carriers have no symptoms.
• You can infect others before you become symptomatic.
• Even those vaccinated can become infected—although usually with milder cases.
• Children can’t yet receive vaccinations.

At-home COVID tests can also be the responsible thing to do if you think you’ve been exposed and don’t want to take a chance on possibly infecting others.

So should you rely on at-home testing?

The answer isn’t simple, and requires some explanation. Here’s what you should know about using at-home tests for COVID-19.

Four types of tests

When we talk about testing, we need to understand that there’s not just one type of test for the coronavirus.  Two must be administered by medical professionals, while two others are available for use in the home.

PCR tests

This is the most reliable form of COVID-19 testing. Polymerase chain reaction (PCR) tests are highly accurate. If done correctly, they can detect the signature pieces of RNA from the virus in the sample. Even so, some studies have suggested that as many as 30 percent of PCR test results are inaccurate. This equals about the same percentage as the standard flu test.

These types of tests require highly trained personnel to administer them. If the sample is not collected correctly, that increases the chances of an inaccurate result. 

Antibody blood tests

These tests do not detect an active infection; rather, they use blood samples to look for antibodies that the body has already activated to combat an infection of COVID-19. That means, at one time, the person was likely infected, but there’s no way to tell if the virus is still active.

In addition, it takes from 10 to 12 days following infection for your body to begin producing antibodies to the virus. This makes antibody tests pretty useless for screening purposes.

They can also show antibodies to the virus if you’ve recently been vaccinated and your body is producing antibodies against a future infection.

Antigen tests

These comprise the majority of the rapid tests available on the market. Like the PCR test, they also require a nasal swab. This looks for traces of the distinctive protein cover on the coronavirus’ cell. These are even more dependent on timing; that is, at what point in the course of infection the person is tested. If it’s too early, the virus may still be replicating itself in the body and has not yet begun to shed detectable pieces of protein.

The results of antigen tests are available sooner than the PCR test—within 10 to 15 minutes. But they are also up to 50 percent less accurate, especially if someone is asymptomatic or early in their infection and has a lower viral load. 

The CDC advises those who test negative on an antigen test to have a PCR test to confirm the results.

Saliva tests

Although not as widely known as the nasal swab tests discussed above, the U.S. Food and Drug Administration (FDA) has approved several saliva-based tests for at-home use. All they require is that you spit into a vial. Then you send it off for analysis and can receive results in as little as 24 hours.

They are more popular with the general public because they are less invasive, cheaper and studies have shown their accuracy is comparable to the PCR test.

A study published last month in the journal PLoS ONE, in fact, showed that one saliva test performed better than some FDA-authorized nasal and oral swab tests. The test, developed at Rockefeller University, not only detected all the positive cases found by the swab tests, but also caught four positive cases that the swabs had missed.

Limitations of all types

As with all types of medical tests, coronavirus tests are rarely, if ever, 100 percent accurate. Much depends on the test’s sensitivity, when in the course of the illness it’s administered, whether the testing procedure was followed precisely, and so on.

Also be aware that, even if a test result is accurate, the moment you come into contact with an infected person, the result is meaningless, because you can then become infected. So please receive a vaccine if you haven’t already, and continue to wear masks in public and practice good hygiene.

Finally, watch out for fake tests. Check the FDA’s website for a list of antigen tests that have received Emergency Use Authorization (EAU).