system
Given the following post, respond as if you're commenting on Reddit:
human
For COVID, What is the range of times from "below the PCR LOD" to onset of fever?

President Trump is reported to have tested positive for COVID Thursday (presumably evening) but also had a fever Friday afternoon.  He also has said he's tested at least daily.  

This seems like a very fast progression.  My understanding is that PCR is sensitive enough to detect at viral loads well below what's necessary to trigger an immune response.  So is 24 hours from negative result to fever within the confidence interval?

I assume a negative test on Wednesday was a true negative, i.e. the viral load was below the limit of detection until Thursday.  I also assume the President's COVID samples are fast tracked so the result is known around 8 hours after the swab.
gpt
Each PCR analyzer is given its own limit of detection. You do a serial dilution of a target and find where you can't detect it anymore. Then you do replicates of the smallest amount you can detect to be sure you can consistently detect it. There are a good number of other proving tests, but you asked for lod.

I know for CLIA monitered states, each individual lab has to do this themselves for laboratory developed test status. Unsure where Trump's samples are being run.