You stated that you wished you could tell them at least a reason for your kidney failure..........well, have they not done a biopsy on you? I don't know the reason for my kidney failure either and they did do a biopsy on me and it just back "inconclusive" and that is exactly what I tell people when they ask I don't know...........the biopsy said, "inconclusive".
But all I can say is, "I found out last year that my kidneys weren't working, and no one knows the cause," and then I always, repeatedly get people asking things like, "Well, what did they do to try to find out?" and then I have to go into my surgical/hospital history. It's just a long process that requires more explaining to the layperson than I wish I had to do.