PSA testing intervals

I was wondering what intervals are recommended while being under Active Surveillance?

I understand that the urologist recommended six-monthly intervals. However, given the variances of PSA tests, and the requirement to establish a useful trend, would it not make more sense to have monthly or bi-monthly tests?

What Steve said, PC is a slow mover. Six month intervals seems the most frequent you'd need.
Andrew

One of the things I learned, or was convinced of, is the importance of having tests conducted/processed at the same laboratory each time.