The FDA just approved the first antibody test for the Coronavirus, made by Cellex. The test has a significant false positive rate though (see here). Now for a lot of tests, false positives can be reduced by retesting positive cases, as the probability of two false positives for the same person is usually low. But this tweet by epidemiologist Zachary Binney raises the possibility that retesting may not help in this case:
Running the test 2x & only telling someone they're immune if they get 2 +s might help reduce false +s, depending on the error source. If it's anything systemic - say it's detecting antibodies from a similar virus that don't grant immunity to COVID-19 - no good.
My question is, is anything known about the sources of error for Cellex’s antibody test, and whether it’s anything systemic along the lines that Binney outlined?