However, since the diagnoses were made by GPs rather than by nephrologists, it is possible
that some CKD diagnoses may not be accurate, notwithstanding our search for specific CKD
codes. For this reason outcome misclassification cannot be completely ruled out. To prevent
misclassification of AKI as CKD during the case ascertainment, CKD codes were only considered
to imply CKD if they were registered more than once.