Internal and external validation
Models were developed and internally validated on the EPaNIC database with tenfold cross-validation. At the external validation stage, models trained on the entire EPaNIC database were applied to the previously unseen external validation cohort to assess generalizability. To examine the model usefulness, model performance was further compared against a reference reflecting the current clinical practice: using as prediction for one-day ahead the same CrCl value of the day of prediction. This reference CrCl was henceforth referred to as 