Help with isolation end date

[LifesTooShortYOLO]

Can anyone clarify when isolation ends for Covid positive PCR test please?
A friends DC had symptoms last Thursday and she got a positive PCR test back today, does the 10 days start from last Thursday which is when the child had symptoms or from today when the results of the PCR came back?
Thanks

From the first symptoms ! Otherwise you would be isolating based on delays in testing

Test and Trace will be in touch to confirm this with her, so leave them to work it out.