Study design and population

This study is part of the TransplantLines Biobank and Cohort Study of the University Medical Center Groningen. In brief, all RTR (aged ≥18 years) with a functioning graft who visited the outpatient clinic of the University Medical Center Groningen between June 2015 and July 2016 were invited to participate. RTR with missing baseline data on CER were excluded. Written informed consent was acquired of all eligible RTR prior to inclusion, and the TransplantLines study protocol was approved by the institutional research board (METc 2014/077), adhering to the declaration of Helsinki. Furthermore, the study protocol is in concordance with the principles of the Declaration of Istanbul as outlined in the ‘Declaration of Istanbul on Organ Trafficking and Transplant Tourism’.16