I’m an engineer so I treat the test results as data. Presumably the results will be compared with previous and future testing and used to decide on a course of action or, if everything is good, intentional inaction.
For the comparison to have the most value, the initial conditions for all tests should be as close to identical as possible. As many variables as possible need to be eliminated.
For example, a quick rise in PSA can mean prostate cancer, or it can mean you had wild sex 8 hours before having your blood drawn, or maybe you have an infection. Unless the initial conditions are the same you cannot compare the two results and responsibly decide on a treatment plan. This is why the Uro will suggest a retest. “Come back and see me in 2 months.”
If you want consistent results, you need to be consistent.