Transplant Renal Artery Stenosis

* To determine the incidence of arterial inflow problems and venous outflow problems as causes of impaired renal function and/or treatment-resistant hypertension after kidney transplantation, when all kidney-transplant recipients in Denmark are evaluated according to uniform, well-defined clinical criteria. * To investigate the efficacy and safety of catheter-based balloon treatment (percutaneous transluminal angioplasty, PTA) for these vascular complications, of which transplant renal artery stenosis is by far the most common. * To assess whether novel imaging and functional diagnostic methods can predict treatment response.