It was possible to identify the precise date of CKD onset because we considered the first registration
of a CKD-related healthcare service to act as a proxy for the former. However, we considered
at least three months and even longer time windows to take into account the possible
lag time between clinical manifestation of impaired renal function and CKD registration. It
was not possible to identify the stage of CKD for the majority of CKD patients as the laboratory
data necessary to stage the disease is not available from Arianna and registered CKD codes
rarely refer to staged CKD.