The hallmark of AKI is a recent increase in creatinine from a previous baseline (if a previous result is available) or a value greater than 1.5x upper limit of the reference interval for age. AKI is usually associated with a fall in urine output.
Following the National Patient Safety Alert for AKI, hospitals are required to issue electronic AKI warning scores. These are based on measurements of serum creatinine (as indicated below). However, these alerts need to be coupled together with appropriate assessment and institution of clinical management plan.
Serum creatinine:
1.5 x baseline creatinine (=previous baseline if known)
1.5 x age specific upper limit of reference interval (ULRI)
(if creatinine between ULRI and 1.5x ULRI, repeat measurement)
Urine output:
| AKI Stage | Creatinine |
| 1 | Measured creatinine >1.5 to <2.0 x reference creatinine/ULRI |
| 2 | Measured creatinine 2.0 to <3.0 x reference creatinine/ULRI |
| 3 | Measured creatinine ≥3.0 x reference creatinine/ULRI |
AKI 1 is often unrecognised. It may represent a physiological response to dehydration, which resolves with appropriate fluid management or may herald more significant intrinsic renal disease, which may progress to AKI 2, and 3. It is important to recognise all stages of AKI and take appropriate action to manage and investigate the cause of AKI.
See “How should AKI be managed to prevent permanent damage?” and “BAPN AKI Management Recommendations” for further management details.