How can you tell if you are having kidney problems? What are the symptoms? My back hurts and urine is darker than normal.

One of the main symtoms is retaining fluid.Mostly in the feet and hands.My husband had the back pain and the dark urine but we didn't know he was in kidney failure until he went to the doctor and his blood pressure was way too high.He went for 6 monthes with his kidneys slowly shutting down.He was sick a lot and we didn't know why.the only way to know for sure is to see your doctor.Don't delay.I don't know if we had discovered my husbands disease earlier if maybe there was something they could have done or not.Knowing is better than not knowing.