[jeremyjh]

It still relies on a population of antibodies for detection. By the time you’ve built a good population of antibodies to trigger the test you will have been contagious for many days. This test is still very valuable though as confirmation of who has antibodies and is likely immune.

[zenexer]

The parent is saying that the antibodies used come from an external source, not from the patient. If what the parent is saying is true, why would the patient need antibodies?