Ashley, Plasma renin tests are done to find out if you are a salt waster or not and how bad (or good) things are currently. I have seen several endo's through the years and my current one is the first (in 20 yrs) to check my renin. If you aren't a salt waster (I'm not) then your renin should be fine. If you are a salt waster however, it is something that needs to be checked regularly in order to adjust your medication (usually florinef) if needed. My doc checks mine every time I have a blood draw (every 3 months) just to be sure. Susan A.