What Cause Dark Urine After Angioplasty?

My mother had an angioplasty a few months ago and has problems with pain in pelvic area and dark urine. She has had alot of tests done and has seen her ob, family and urology doctor. All say that she is fine except for a small polyp in her urethra. She is still concerned and so am I. She has had an ultrasound, a procedure using dye to test the bladder and blood work. Do you have any suggestions?