Thanks, @MelissaKariWard, for capturing the since deleted tweets. This is why I expressed concern.
To explain, we use PCR (swab) tests to detect acute infections (it tests for viral particles). A concern with PCR tests is that you can get false negatives, where you are actually infected but the test comes back negative. This is bad because you may act as if you are uninfected.
Antibody tests look for presence of different antibodies in your blood. It takes time for your body to mount an immune response (1-3 weeks). Thus, they are not used to detect acute infections. Instead, they are used to detect evidence of prior infection.
An advantage of antibody tests is that they can (mostly) detect prior infections in people who didn’t even have symptoms, so were missed by PCR testing. A disadvantage of these tests is they can return false positives. Someone thinks they are immune and adopts riskier behavior.
It is unclear to me why false negative antibody tests would present an important risk. If you think you are still susceptible to infection (even though you really had been infected before), you would behave more cautiously.
What concerned me was the talk about transmitting to others, which suggests using antibody tests to test people who are actively infected. Of course someone could be recently infected, not know it, and get a negative antibody test, but this would be rare in the scheme of things.
