Measuring testosterone is complicated, because the tests themselves aren't always reliable, and results can differ from one lab to the next. "Normal" levels can also vary dramatically from one man to the next. And they can vary from minute to minute in the same man; testicles seem to do everything in spurts. That's because testosterone levels fluctuate with the little wins and losses of daily life. So if a test suggests that you have a testosterone problem, do not despair: There's a one-in-three chance you'll be back to normal on a follow-up.