What are the error modes of waiting too long to read a rapid antigen test? Does this increase the probability of the user reading a false positive, false negative, or both? How does this depend on time?

I currently am interested in results from a BinaxNOW kit, but I've used several brands and they all work more or less the same way, so I suspect that this generalizes.

What is the relationship between test failure modes and time after the recommended reading interval?

  • 1
    As you know, prior research is required here, so what has your research revealed so far? And please spell out what you mean by $t$. Acronyms, non-obvious abbreviations, and technical jargon should always be spelled out on first use.
    – Carey Gregory
    Jul 4, 2022 at 3:36
  • Everything I've found simply describes results after the given time interval as "invalid".
    – Him
    Jul 4, 2022 at 4:18
  • 6
    The tests are only validated for the given time interval, so the answer is "no one knows". In theory, if the antibody is not specific enough, giving it longer time to pick up "false antigens" would increase the false-positive rate. But the answer is probably that no one bothered checking. This is why the testing procedures are standardised
    – Narusan
    Jul 4, 2022 at 8:03
  • 3
    The problem isn't that it's inappropriate for this site. It is on topic, as you pointed out. The trouble is that in medicine there are many questions that can't be answered, or at least not without a very deep dive into very complex research that requires someone with a specific background to answer. Just to make sure this isn't an XY problem, let me ask what your motivation is for this question. What problem are you trying to solve?
    – Carey Gregory
    Jul 4, 2022 at 22:13
  • 1
    In my experience, every single test that I've taken has kept the same readouts for at least 24 hours after the read window has expired. That is, if I check it at the recommended 15 minute mark and at 24 hours + 15 minutes, the test still shows the same result. Jul 5, 2022 at 0:46


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