This study examined WRF occurring during the first 4 days of hospitalization, defined as a creatinine increase of ≥0.3 mg/dL (26.5 µmol/L), at any time between day 1 (baseline) and day 4, or initiation of hemofiltration as it was defined in the main study. Sensitivity analyses were performed with other definitions, including absolute creatinine, a relative creatinine increase of ≥25%, a combined increase of ≥0.3 mg/dL and ≥25%, and various cut-offs.