FDA Approves new serological test.

https://www.yahoo.com/lifestyle/coronavirus-antibody-test-203521083.html

This is an important step forward. Having this test, and using it appropriately, is much better than nothing. It is also important to know the performance of the test, which is not perfect. However, as Voltaire famously observed, "The perfect is the enemy of the good."

Based on the reported testing on the packaging, it is about 93.8% sensitive [CI: 88.2-96.8] and about 96% specific [CI:92.8-97.8]. If it is used in a population where a history of true infections is less than 10% then more than 28% of the positive tests are expected to be false.

So if you have no strong history of exposure and illness, you should not view a positive IgG test as a superpower. If you live near Boston, and you had a flu-like illness before the super-spreading event of the February 26 Biogen conference at the Long Wharf Hotel, then it almost certainly wasn't COVID-19.

Also, some people who make IgG antibodies don't make one that is good enough to fight off the virus, and it might even make the virus worse. There is a theory that a weak IgG antibody fuels the dreadful downturn some COVID-19 patients have in the 7-14 day period, after seeming to do well. This is a well-known phenomenon in virology. There are other viruses that can hijack weak antibodies to make the illness worse. It has been the downfall of several vaccine development programs where the vaccine induced antibodies that made people sicker if they got the targeted virus.

Here is a link to the product package info:
https://cellexcovid.com/wp-content/uploads/2020/04/Cellex-rapid-ifu.pdf