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Are rapid tests useful, even if not always accurate?

Question: I just got a text from an urgent care provider saying they are now offering “FDA authorized Covid-19 Rapid Testing, results in 15–20 minutes!” I’ve read previously that rapid tests can give a significant number of false positives and false negatives. Do you have current information to provide on this, and also any guidance on whether or not the rapid tests are useful even if not always accurate?

Answer: I think the test your urgent care provider is referring to is the new Abbott BinaxNow antigen test, which received FDA emergency use authorization in late August. We discussed different test types most recently in our Q&A of 9/4 #Test Types, and the table shared in that post provides an overview of the three test types — molecular (e.g. PCR), antigen, and antibody. Overall, antigen tests are a great addition to our testing menu because they:

  • Are inexpensive (ex: Abbott is selling its new test for $5)
  • Are simple for healthcare workers to use (ex: the Abbott test is the size of a credit card and requires no additional equipment like an analyzer)
  • Provide results quickly (ex: new Abbott test provides results in 15 minutes)
  • Are designed to detect active SARS-CoV-2 infection

In short, these new antigen tests allow us to make COVID-19 testing more widely available, with results provided more quickly than traditional molecular/PCR testing (yay!).

But it’s not all sunshine — you’re right to remember that different tests also have drawbacks. For antigen testing, positive results are generally very accurate (e.g. if the test tells you you’re positive, you’re really positive), but negative results are not as accurate (e.g. a negative antigen test cannot rule out active infection). Re-stated, with antigen tests, you’re unlikely to get a false positive, but there’s some chance of a false negative (and for a refresh on sensitivity/specificity see Q&A of 4/15 #Sensitivity). So if you and/or your healthcare provider believe that you may be infected with SARS-CoV-2 and an antigen test comes back negative, you’ll need to have a molecular/PCR test too.