Synopsis
Recognise acute kidney injury promptly, apply creatinine and urine-output staging correctly, identify immediate threats and start a cause-directed assessment before reversible injury progresses.
- Diagnose AKI in an adult when serum creatinine rises by at least 26 micromol/L within 48 hours, rises to at least 1.5 times a known or presumed baseline within 7 days, or urine output falls below 0.5 mL/kg/hour for more than 6 hours.
- Use the worst KDIGO creatinine or urine-output criterion. Stage 1: creatinine 1.5–1.9 times baseline or a rise of at least 26 micromol/L; urine output below 0.5 mL/kg/hour for 6–12 hours. Stage 2: creatinine 2.0–2.9 times baseline; urine output below 0.5 mL/kg/hour for at least 12 hours. Stage 3: creatinine at least 3 times baseline, an increase to at least 354 micromol/L with an acute rise of at least 44 micromol/L, or initiation of renal replacement therapy; urine output below 0.3 mL/kg/hour for at least 24 hours or anuria for at least 12 hours.
- Creatinine is a delayed concentration marker influenced by muscle mass, fluid balance and laboratory timing; an apparently normal result cannot exclude evolving injury after shock, sepsis or toxin exposure.
Key red flags
A rise of at least 26 micromol/L within 48 hours or at least 50% above baseline within 7 days meets an adult AKI criterion. Search laboratory records for a credible baseline and state whether the timing is known, estimated or uncertain.
Investigation priorities
Confirm an acute change, stage severity and expose dangerous potassium or bicarbonate disturbance.
Management branches
A laboratory alert, new oliguria or clinical suspicion of acute renal dysfunction.
- 1. Perform ABCDE, obtain observations, assess perfusion and congestion, verify urine output and check the catheter or bladder when relevant.
- 2. Send urgent creatinine, electrolytes and venous gas, obtain an ECG if potassium may be raised, and begin treatment of any immediate physiological threat.
Key medicines
Balanced isotonic crystalloidGive a cautious bolus only when clinical assessment supports intravascular depletion, then reassess immediately; use the current local resuscitation protocol rather than a fixed cumulative volume.