psa tests

Just had my 3 mo and results were very good less than .05 which is as low as their tests went.I travel 4 hrs to the location of my operation Dr. stated since I live so far and everything went so well after my Davinci to have my psa checked every 3 mo near home. My question is since testing vary so much,like less than .1 from one location to .05 at another and now i've read of ulta sensitive.I would like to know which equipment, test lower and best so i know what to ask the labs