Our society has a pattern of thriving on instant gratification. Whether it's rushing our online orders to receive them faster or searching for a quick diagnosis on WebMD every time our head hurts, patience is currently at an all-time low. With over 40 million cases of coronavirus in the U.S. alone since the start of the pandemic, that sense of impatience extends now to a desire to know ASAP whether we or a loved one might be infected with COVID-19. Little wonder that self-testing for COVID at home has become an attractive option for many. But how reliable are these tests?
Before we can answer that, let's look at the different ways in which we can detect COVID-19. Currently, there are three main methods to test for the virus including an antibody test, a polymerase chain reaction (PCR) test, and an antigen test.
An antibody test, as the term suggests, looks for antibodies in your bloodstream that can help determine if you've previously been infected with the virus. This type of test typically requires you to go to a clinic or lab and get your blood drawn. Depending on the testing site, you could get same-day notification of the results, unless further lab analysis is needed, in which case it may take a few days. The accuracy of antibody tests compared to other testing methods is somewhat unclear. According to the CDC, a single antibody test may not be enough to accurately determine whether an individual has had a prior infection or has antibodies to the virus. A second antibody test is recommended to verify the results. The uncertainty of the test also extends to vaccinated individuals who may test positive due to their bodies generating antibodies in response to the vaccine.
The other two types of tests are known as viral tests, which rely on a sample from an oral or nasal swab. PCR tests, like antibody tests, are also generally performed in the lab by a medical professional. As you'll see, many experts consider them the most accurate and reliable form of COVID-19 testing available to the public. Turnaround can be as quick as 24 hours, but you won't get immediate results.
Which is why at-home rapid tests are understandably growing in popularity. Rapid tests detect the virus by looking for antigens, proteins located on the surface of the virus. The speedy results of this form of testing have made it a go-to choice for many. Currently, three brands of at-home rapid tests have received emergency authorization from the FDA including Abbott's BinaxNow, the Ellume COVID-19 home test, and Quidel QuickVue. While these at-home kits may be the first choice for anxious individuals wanting a quick answer, we must also consider what the results mean and how much we can rely on these tests to determine whether we've truly been infected.
Discover spoke to Pia MacDonald, an infectious disease epidemiologist and public health researcher, to address the pros and cons of at-home and other COVID-19 tests.
Q: Are most at-home COVID-19 tests rapid tests? What would you say is the accuracy of these tests?
A: At-home tests that provide results without sending the samples to a laboratory are all antigen tests, which are synonymous with rapid tests. Antibody and PCR tests still require you to visit a health professional rather than using a home test kit at this point.
There are many different rapid test kits available now and their accuracy will vary widely. Most have not yet been tested rigorously or extensively in various settings such as homes, workplaces and schools. Generally, antigen tests tend to be more accurate if a person has COVID-19 symptoms. They are considered less accurate if a person does not have any symptoms of being infected with the virus.
Q: Could you explain the scientific process behind how rapid tests work? How is this different from PCR COVID tests?
A: A rapid test looks for pieces of protein from the SARS-CoV-2 virus. Therefore, a positive test is dependent on the collected specimen having enough protein to be detectable with the home test kit. Home test kits are not standardized, so one may need more or less detectable protein to result in a positive or negative test. Getting enough protein to be detectable will be dependent on the specific test used, the quality of the specimen collected from a person and the amount of virus the person has in their body. False negatives will be more common than with a PCR-based test. This means that a person might take a home test and be negative, but really be infected with the virus.
A PCR test looks for genetic material from the virus, and the laboratory processing of the sample includes the amplification of genetic material so that the chance of detecting it, if it is there, is very good. Therefore, there is less dependency on the quality of the specimen collected and/or amount of virus a person has, as compared to an antigen test. False negatives will be less common with a PCR test than with an antigen-based test. This means a person who gets a PCR test and is negative can be more confident they are not infected with the virus.
Q: How do you generally use at-home test kits?
A: Home test kits require a person to collect a specimen of bodily fluid from either the nose or throat using a sterile swab. There is then a second step where a person adds a solution to the swab and lets the swab and solution sit for a specified time before a result appears. There are similarities with a home pregnancy test.
Q: Do at-home COVID-19 tests currently have the capability to detect the Delta variant?
A: The home test can detect an infection of the virus, including the Delta variant, but home tests are not set up to differentiate variants. This means that a home test will not indicate what variant a person is infected with.
Q: What advice do you have for people using at-home COVID-19 test kits? How should they interpret their results?
A: People using home test kits should read and follow the instructions very carefully. A negative test should be interpreted with caution since the risk of a false negative is possible. A PCR test that includes laboratory processing will be more reliable and accurate, even though getting results may take longer than the rapid antigen test. In situations where it’s really critical to know if a person is infected with SARS-CoV-2 or not, a PCR test is better.
