Vascular Complications After Kidney Transplantation

Inclusion Criteria: 1\. At least one of the following clinical criteria (1 or 2) must be fulfilled: 1. Graft dysfunction, defined by at least one of the following: * Acute reduction in estimated glomerular filtration rate (eGFR) \>15% on two consecutive measurements at least 2 weeks apart, with other causes excluded (rejection, obstruction, infection). * eGFR \<50% of the expected value 30 days after kidney transplantation of unknown cause. * Decline in eGFR \>30% after initiation of an angiotensin-converting enzyme inhibitor or angiotensin II receptor blocker. 2. Persistent resistant hypertension for more than 6 weeks after kidney transplantation, defined as: * 24-hour ambulatory systolic blood pressure \>130 mmHg despite treatment with at least three classes of antihypertensive medication at maximally tolerated doses (including diuretics, if tolerated). Together with at least one of the following radiological criteria: 1. CT or MR angiography demonstrating a lumen reduction ≥50%. 2. Doppler ultrasound showing: 1. Peak systolic velocity in the renal artery ≥200 cm/s and a renal renal ratio (velocity at stenosis / velocity in distal artery) \>4. 2. Acceleration time \>70 ms in intrarenal arteries. 2\. In cases of strong clinical suspicion of a vascular complication where CT or MR angiography cannot reliably exclude graft artery or vein stenosis, patients may be referred for confirmatory invasive investigations. Before PTA, catheter-based angiography and translesional pressure measurements are performed to confirm whether the patient meets the radiological eligibility criterion for PTA: 1. Stenosis ≥70%. 2. Stenosis 50-69% if at least one of the following criteria is met: * Mean translesional pressure gradient ≥10 mmHg. * Systolic pressure gradient ≥20 mmHg. * Renal Pd/Pa ≤0.8. * If pressure measurements cannot be obtained, treatment is based on the operator's clinical judgement. Exclusion Criteria: 1. Inability to provide informed consent. 2. Concurrent biopsy demonstrating rejection requiring treatment. 3. Pregnancy. 4. Previous PTA of the same vessel. 5. Patients unable to tolerate any form of antithrombotic therapy and therefore not eligible for stent placement.