Renovascular Hypertension

* 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.

The goal of this clinical trial is to document a beneficial effect of percutaneous transluminal renal angioplasty (PTRA) of atherosclerotic renal artery stenosis in high-risk patients selected according to the criteria used in the DAN-PTRA study. The main questions the trial aims to answer are if renal artery stenting compared with optimal medical treatment alone has beneficial effects on: * Blood pressure * Kidney function * Hospitalizations for heart failure