I Am A 52 Year Old Woman That Keep Having

I am a 52 year old woman that keep having protein in my urine, when my urologist check my urine. He did tests but did find anything, then I was referred to the kidney doctor and tests was also done and it was the same response he also found nothing, but told me he would just watch it and see. What would you say to this do you think it is serious and I should be worried? Your response is greatly appreciated.