I think many are confused here... There are three basic kinds of tests in common use. The PCR, The Antigen test and the Antibody test.
Needless to say, the PCR is considered the Gold Standard. But again I should say that this is not totally perfect.
But also note there are very high sensitivity PCR machines that are near 100% accurate.
The PCR looks for genetic material from the Covid virus, whereas the Antigen tests look for proteins that live on the virus’ surface. This is much easier to do, not much chemistry is involved but there is a
trade-off. ie. it's
less sensitive.
False positives are less with antigen tests, but as many as
50% of negative results are reportedly inaccurate. As I mentioned previously this is dangerous. A false positive places the person in isolation , no harm done other than inconvenience. But a false negative can place many others in danger.
The antibody is quite different. This is not intended to pick up on current Covid infection. Rather, they search the blood for antibodies, proteins the body makes in response to an infection. These tests look for Covid specific antibodies to check if you’ve previously had coronavirus. So this kind of test has little diagnostic value, other than to confirm that you have had Covid.
Note that countries like South Korea, New Zealand & Australia totally depend on PCR tests and quite effectively run these tests to provide results in 24 hours.
This is a graphic on how these tests work. Probablity of detection vs Time.
