Quote Originally Posted by Muddy Retriever View Post
I've thought that myself too. In some cases people are tested again. Look half way down this under the heading The Number of People Tested. One of the reasons it gives for people being tested more than once is:

"individuals with early symptoms who test negative, develop more symptoms and are retested and found to be positive"

https://www.gov.uk/government/public...thodology-note

But I imagine there will be many others who aren't tested again. If everybody was tested twice then the chances of a false negative would be only 4% assuming the false negative rate of one test is 20%. But I would think there is not the capacity to do that at the moment.
On your link.

This means that currently all positive cases identified by pillar 4 surveillance studies (for antigen testing) are captured under pillar 1 or 2.

Which seems to indicate that someone with anti-bodies is a positive case. Even if they had been infectious a few weeks or months earlier.