The 3C study is a randomised trial investigating different immunosuppression strategies in kidney transplantation. It recruited 852 participants between 2010 and 2013 and these participants are now under long-term follow-up through registries to allow the trial to assess the long-term risks and benefits of the different treatments. A key outcome is transplant function, which is assessed from creatinine measurements done routinely as part of transplant care and collected by the UKRR. These data are critical to the long term assessments.