A friend pointed out that there is cross-reactivity of most coronavirus antibody tests. That means if you recently had a cold caused by a coronavirus (not COVID-19, but one of the four common cold strains), then you may test positive on this test, even though you don’t have COVID-19. We have known that this is a problem with these tests. How big of a problem? I looked into it further because the friend pointed it out.

The study says that they used a test kit from Premier Biotech in MN, an American company. So I assumed that it was probably pretty good, like the Abbott antibody test. But no. Premier Biotech is simply a distributor of an antibody test from Hangzhou Biotest Biotech in China.

Here is the sell sheet from Hangzhou Biotest Biotech. The plot thickens!