Hi Sarah, my son's potassium seem normal 4.3mmol/L ref range 3.5 - 5.3, he has not had urine sodium checked as far as I can remember! Hi IceLizard, my son does do light cardio exercise when he can, in the the shape of drumming, TRX and stationary bike on not good days he does leg work with those big elastic bands. My son has tried fludro 2 -3 times to no avail and midrodine (SP?) 2 times bad reaction to it both times. Hi Rachel, I have booked an appointment with GP to get back on track as it is just not fair to my poor son if I don't try and find out what is going on. Hi Arizona Girl, you are so right about fighting in my son's corner and I will keep on until we get somewhere. Ha ha poor Dr. does not know what lengths a mother protecting her children will go to.