The answer is it depends on the brand of the test. Here’s what you need to know.

Here’s what you need to know about antigen rapid tests:

1. In general, each test brand will test for a specific antigen. They may or may not tell you which antigen they detect.
2. Each brand has a different sensitivity. For low sensitivity tests, it will be fruitless to test if you are not symptomatic because it will almost certainly be negative. It would be nice if they correlated the results with PCR cycle thresholds, but those are non-standard as well.

Unfortunately, as far as I know, there are no standards to inform you on 1 and 2 above. There is no “reference standard” that they compare to.

This of course means that you can be wasting serious money taking tests when you are asymptomatic because the certain brands will never be positive if you are asymptomatic. I want to thank Dr. Byram Bridle for pointing this out to me.

They really should tell you, “Hey, if you aren’t symptomatic, don’t bother to take our test.” The manufacturers are never going to tell you that (since they aren’t required to), but I thought you should know.