My understanding of the tests is they are very accurate at determining if somebody has a lot of virus, but not at detecting lower thresholds of virus. So compa

My understanding of the tests is they are very accurate at determining if somebody has a lot of virus, but not at detecting lower thresholds of virus. So compared to PCR tests, they have a lot of false negatives. The Abbott ID NOW COVID-19 rapid result machine that the white house uses has the same properties: > Based on our findings we could argue that the Abbott ID NOW detects samples with high viral load or possibly viable virus that could be of importance for transmission. But, the fact that it misses positive samples on patients being admitted to the hospital with clinical picture of COVID-19 makes this technology unacceptable in our clinical setting [1] So they will have very few false positives, but a lot of false negatives. However... being negative for having a lot of virus is actually meaningful, whether you have the virus or not, because the best assumption is that contagiousness is related to amount of virus in your system. So basically, the tests aren't perfectly accurate, but they do provide useful information, and they are instant. That is the key. A PCR test that is perfectly accurately is useless for contact tracing/isolation and peace of mind if it takes 14+ days to get the results. Think of a pregnancy test. If it comes back positive, you are very likely pregnant but should get it confirmed by a doctor. If it comes back negative, you likely aren't pregnant, but maybe it's too early to tell. Pregnancy tests are widely used even though they have these characteristics because people understand the quirks and the information they provide is useful and of course, comes instantly. 1: https://www.biorxiv.org/content/10.1101/2020.05.11.089896v1.full https://www.biorxiv.org/content/10.1101/2020.05.11.089896v1....