Definition and epidemiology
Acute kidney injury (AKI) is an abrupt fall in glomerular filtration over hours to days, captured by a rise in serum creatinine and/or a fall in urine output. KDIGO unified the earlier RIFLE and AKIN systems into a single staged definition. AKI is present when serum creatinine rises by ≥0.3 mg/dL (≥26.5 µmol/L) within 48 hours, rises to ≥1.5 times baseline known or presumed to have occurred within the prior 7 days, or urine output falls below 0.5 mL/kg/h for 6 hours.
AKI complicates a substantial fraction of pediatric intensive-care and post-cardiac-surgery admissions; the landmark AWARE study found AKI in roughly a quarter of critically ill children, with severe AKI independently associated with mortality. Even a single stage-1 episode is linked to longer stay and later chronic kidney disease, so detection is not academic.
Clinical features
AKI is often clinically silent and detected only on biochemistry. Look for oliguria/anuria, fluid overload (weight gain, oedema, hypertension, pulmonary congestion), and features of the underlying insult — hypovolaemia, sepsis, nephrotoxin exposure, or obstruction. Uraemic symptoms (lethargy, vomiting, encephalopathy) and the metabolic consequences (hyperkalaemia, metabolic acidosis, hyperphosphataemia, hypocalcaemia) appear as injury advances. Causes are grouped as pre-renal (volume depletion, low cardiac output), intrinsic (acute tubular necrosis, glomerulonephritis, interstitial nephritis, HUS, nephrotoxins), and post-renal (obstruction) — a framework that drives the workup.
Diagnosis and staging
Establish a baseline creatinine, quantify urine output (catheter or strict input/output), and stage by whichever of the creatinine or urine-output criteria is worse:
- Stage 1: creatinine 1.5–1.9 × baseline or ≥0.3 mg/dL rise; or urine output <0.5 mL/kg/h for 6–12 h.
- Stage 2: creatinine 2.0–2.9 × baseline; or urine output <0.5 mL/kg/h for ≥12 h.
- Stage 3: creatinine ≥3 × baseline, or ≥4.0 mg/dL, or initiation of renal replacement therapy; or — in patients <18 years — a fall in eGFR to <35 mL/min/1.73 m²; or urine output <0.3 mL/kg/h for ≥24 h, or anuria for ≥12 h.
Workup: urinalysis and microscopy, fractional excretion of sodium/urea, renal tract ultrasound (exclude obstruction), electrolytes, and cause-specific tests (complement, ANA/ANCA, blood film and LDH for HUS) when intrinsic disease is suspected.
See the full criteria: KDIGO Acute Kidney Injury Staging
Red flags
- Hyperkalaemia with ECG changes — peaked T waves, widened QRS
- Anuria, fluid overload with respiratory compromise, or refractory hypertension
- Severe metabolic acidosis or uraemic encephalopathy
- Thrombocytopenia, haemolysis and AKI together — think HUS/TMA
- Rapidly rising creatinine with active urinary sediment — rapidly progressive glomerulonephritis
- Failure to respond to volume resuscitation — escalate for possible renal replacement therapy
Management overview
There is no specific pharmacotherapy that reverses established AKI; management is supportive and cause-directed. Restore and protect perfusion with judicious isotonic fluids, treat sepsis, and relieve obstruction. Stop or dose-adjust nephrotoxins (aminoglycosides, NSAIDs, iodinated contrast, calcineurin inhibitors) and renally cleared drugs. Manage hyperkalaemia with the standard stepwise approach (membrane stabilisation, intracellular shift, removal), correct acidosis, and control hypertension and fluid overload — loop diuretics may aid fluid management but do not treat the AKI itself. Indications for renal replacement therapy are refractory hyperkalaemia, acidosis, fluid overload, or uraemic complications. Early pediatric nephrology involvement is warranted for intrinsic disease, dialysis need, or diagnostic uncertainty. Survivors of severe AKI need long-term renal follow-up given the risk of chronic kidney disease.
References
- KDIGO. Kidney Int Suppl. 2012;2:1–138.
- Akcan-Arikan A, et al. pRIFLE. Kidney Int. 2007;71:1028–1035.
- Palevsky PM, et al. KDOQI US Commentary. Am J Kidney Dis. 2013;61:649–672.
Decision support for qualified clinicians only — verify against current primary guidelines and your clinical judgement.