Q: I heard that the FDA approved several new rapid home test for diagnosis of COVID-19. Are the rapid tests just as good as the others? Can I take this one before I visit family?
A: TL; DR: No, rapid tests are not quite as good at picking up positives (someone who really has COVID-19) as the gold standard PCR test.
Testing is a key strategy in controlling the spread of SARS CoV-2 and over 200 tests have been authorized this year, with nearly 25 tests with home sample collection. In-home testing could help us test more individuals in the U.S. and worldwide by decreasing barriers to testing like finding a test site, waiting for results, and/or requiring a provider’s order for testing. Indeed, some experts believe that rapid tests are at the heart of controlling this pandemic. However, there are a couple of things that should be considered before one goes out and gets a test.
⚗️ Testing: There are two categories of tests-diagnostic and antibody. Diagnostic tests tell you if you have an active infection and antibody tests may tell you if you have had previous infection. Diagnostic tests can be either molecular or antigen tests. Molecular tests include PCR, which detects the viral genome. Antigen tests detect proteins on the surface of a virus. (info on types of tests) The rapid tests now available are categorized as diagnostic tests.*
📑 A positive result on a PCR test is usually accurate and does not need to be repeated. A positive result on an antigen test is usually correct but may need to be repeated. If you have a positive result, you should follow CDC recommendations. A negative result on an antigen test MAY STILL require follow up with a PCR test. If you have a negative result but are concerned that you may have COVID-19, you should follow up with your primary care provider (especially if you are symptomatic).
RAPID TESTS: There are a number of new rapid tests that allow an individual to collect a home sample and either test themselves or drop a sample off at a lab. The Ellume test is one of the most recent and specifically differentiates itself from other rapid tests because it has some evidence for use in asymptomatic people (previously rapid tests were criticized for evidence suggesting they were less accurate in asymptomatic individuals). It is also cheaper than others and does not require a prescription.
However, rapid tests are not as good at picking up positive cases as PCR tests (or negative cases for that matter). Someone who is truly positive could have a negative test, go about their life, and infect other people prior to developing symptoms. Someone who tests positive but is really negative may face unnecessary isolation and even risks (for example being placed on a COVID-19 floor in a residential facility when not positive). This is a downside of rapid tests-there can be less diagnostic accuracy. So it is better to stick to molecular tests (like PCR) if you are testing prior to visiting family (and of course following all appropriate safety guidelines). Rapid tests work best when used repeatedly and consistently to monitor individuals and populations on a larger scale (think nursing home residents, college students, or NBA players). But, even when done well, there can still be errors.
BOTTOM LINE: Rapid tests, even the new ones, can’t replace PCR testing, nor can they replace good public health measures to reduce the transmission of SARS-CoV-2. We still need more research (and more widespread testing) to determine if newer in home tests can be effective in helping to test a wider population and consequently decrease the spread of SARS-CoV-2. Rapid tests could be helpful if an individual would benefit from isolating and/or when there is a known exposure. There are other considerations as well, including cost, access, and supply. At the moment, the increasing development of tests is yet another ray of hope in the effort to control the spread of this pandemic. But one that we should meet with cautious optimism.
Stay safe. Stay sane.
Those Nerdy Girls
*This name can be misleading. This suggests that the test tells if you have active infections, but based on evidence is better used for monitoring rather than diagnosis.
Prior posts on testing: