I don’t know about protocol, but you are doing great eight years later.
Is it a problem for you to give blood for PSA tests? I just nip to my local chemist and the result comes up on my iPad EMIS Patient Access app around 8.30 next morning.
Six months, twelve months? If you haven’t got cancer stick with the annual testing, or not. Your choice.
Best wishes.
Cheers, John.