Transplant renal artery stenosis (TRAS) is abnormal narrowing of the main blood vessel to the kidney transplant and has historically been considered a surgical complication. In heart transplantation, it has long been recognised that rejection can cause narrowing of the heart's blood vessels, and that this complication is the leading cause of heart transplant failure. It is reasonable to assume that this process may also occur in kidney transplantation, which could contribute to premature transplant failure. However, in kidney transplantation it is also likely that other factors, such as surgical factors, traditional cardiovascular risk factors and immunological factors, contribute to the development of TRAS. Given that the disease processes that cause TRAS are not fully understood, at present there is no consensus among kidney doctors on the best means of treating patients diagnosed with TRAS. The aim of the proposed study is to investigate the involvement of these different processes in the development of TRAS, and investigate the optimal way to diagnose and manage TRAS.

At present, there is no standard recommendation for how to treat patients with TRAS. This is partly due to the fact that patients with TRAS may have a broad array of symptoms: Some may have no symptoms, other may have problems with high blood pressure or fluid accumulation, and others may have severe transplant dysfunction. In most transplant centres, patient TRAS and severe symptoms will undergo IADSA and a stent will be placed to open the narrowing. However, it is not clear how best to manage patients with TRAS who have mild to moderate symptoms. We propose to recruit 36 such patients to a clinical study and split them into two groups: One group to undergo IADSA with possible stent placement, and one group to be closely observed. We will then compare transplant function, and other outcomes, after one year between the two groups.

Transplant renal artery stenosis (TRAS) is abnormal narrowing of the main blood vessel to the kidney transplant and has historically been considered a surgical complication. In heart transplantation, it has long been recognised that rejection can cause narrowing of the heart's blood vessels, and that this complication is the leading cause of heart transplant failure. It is reasonable to assume that this process may also occur in kidney transplantation, which could contribute to premature transplant failure. However, in kidney transplantation it is also likely that other factors, such as surgical factors, traditional cardiovascular risk factors and immunological factors, contribute to the development of TRAS. Given that the disease processes that cause TRAS are not fully understood, at present there is no consensus among kidney doctors on the best means of treating patients diagnosed with TRAS. The aim of the proposed study is to investigate the involvement of these different processes in the development of TRAS, and investigate the optimal way to diagnose and manage TRAS.

At present, there is no standard recommendation for how to treat patients with TRAS. This is partly due to the fact that patients with TRAS may have a broad array of symptoms: Some may have no symptoms, other may have problems with high blood pressure or fluid accumulation, and others may have severe transplant dysfunction. In most transplant centres, patient TRAS and severe symptoms will undergo IADSA and a stent will be placed to open the narrowing. However, it is not clear how best to manage patients with TRAS who have mild to moderate symptoms. We propose to recruit 36 such patients to a clinical study and split them into two groups: One group to undergo IADSA with possible stent placement, and one group to be closely observed. We will then compare transplant function, and other outcomes, after one year between the two groups.

Inclusion Criteria:

- 1. Renal transplant recipient with a diagnosis of TRAS by radiological imaging, and an MDT decision to proceed with diagnostic IADSA.

2. Aged 18 years and over 3. Able to give informed consent

Exclusion Criteria:

- 1. Estimated GFR <10mls/min/1.73m2 or dialysis dependence 2. Contraindication to angiography (e.g. allergy to radiological contrast) 3. Patients with clinical features of severe TRAS (eg. resistant hypertension, pulmonary oedema and/or rapidly deteriorating function).

4. Any condition or co-morbidity which in the investigator's opinion would make the patient ineligible for the trial or unlikely to adhere to trial procedures.