Acute Kidney Injury in Children
On this page
Direct answer
Acute kidney injury in children is an abrupt fall in kidney function, defined by a serum creatinine rise of at least 0.3 mg/dL within 48 hours or urine output below 0.5 mL/kg per hour for six hours or more. Prerenal causes such as hypovolaemia, sepsis and cardiac failure account for many cases, and FEUrea helps separate them from intrinsic acute tubular necrosis. Indications for dialysis include refractory hyperkalaemia, acidosis, fluid overload and uraemic complications.
What you must remember
- pRIFLE: paediatric RIFLE grades Risk, Injury and Failure by eGFR decline of 25, 50 and 75 per cent, plus urine output criteria.
- KDIGO staging: stage 1 is creatinine 1.5 to 1.9 times baseline or a rise of 0.3 mg/dL; stage 3 includes creatinine 4 mg/dL or more, eGFR below 35 mL/min per 1.73 m2 in under 18s, or dialysis.
- Prerenal: hypovolaemia, sepsis, cardiac failure, haemorrhage, NSAIDs and ACE inhibitors; FEUrea below about 35 per cent.
- Intrinsic: acute tubular necrosis (muddy brown granular casts), interstitial nephritis (white cells and eosinophils), glomerulonephritis (red cell casts) and haemolytic uraemic syndrome.
- Postrenal: obstruction from posterior urethral valves, stones or bladder outlet problems; ultrasound of kidneys and bladder is mandatory.
- Fluid assessment: volume depletion needs isotonic bolus with reassessment; oliguric children are at risk of overload.
- Dialysis indications: refractory hyperkalaemia, metabolic acidosis, fluid overload with respiratory compromise, uraemic pericarditis or encephalopathy, and severe drug toxicity.
- Nephrotoxins: avoid aminoglycosides, NSAIDs, contrast and ACE inhibitors during AKI; dose drugs for current GFR.
A stepwise approach to the oliguric child
A 4-year-old with gastroenteritis is passing very little urine, and creatinine has risen from baseline over two days. The sequence below separates a reversible cause from one that needs urgent treatment.
- Confirm the injury. Compare with baseline creatinine, remembering that creatinine lags behind true GFR loss, so the trend matters.
- Assess volume status. Examine for hypovolaemia and weigh the child; record fluid balance hourly.
- Exclude obstruction. Ultrasound of kidneys and bladder, with bladder scan or catheter where needed.
- Test the urine. Microscopy for casts, urine sodium, FEUrea and protein-creatinine ratio.
- Look for urgency. Check potassium, bicarbonate, calcium and ECG changes.
- Treat and support. Correct the cause, stop nephrotoxins, dose drugs for GFR and start nutrition.
- Plan follow-up. Episodes of AKI raise the later risk of chronic kidney disease.
Where the exam tries to catch you
AKI questions reward careful reading of the urine and the trend.
- Trap: using FENa in a child receiving diuretics. Correct: diuretics increase sodium excretion, so FEUrea is the more reliable index.
- Trap: treating a raised creatinine as the current GFR. Correct: creatinine lags, so the trend and urine output indicate the present kidney function.
- Trap: giving furosemide to reverse oliguric AKI. Correct: diuretics do not prevent or shorten AKI; they only manage fluid overload.
- Trap: missing obstruction in a boy with oliguria. Correct: posterior urethral valves must be excluded with bladder ultrasound.
Frequently asked questions
What creatinine rise defines KDIGO stage 3 acute kidney injury?
KDIGO stage 3 acute kidney injury in children includes a creatinine of three times baseline or more, or 4 mg/dL or more. An eGFR below 35 mL/min per 1.73 m2 in a child under 18, or the need for dialysis, also defines stage 3.
Why is FEUrea preferred over FENa in a child with acute kidney injury on diuretics?
FEUrea is preferred over FENa in a child with acute kidney injury on diuretics because diuretics increase sodium excretion and distort FENa. Urea handling is less affected, so FEUrea below about 35 per cent suggests a prerenal cause.
Which urine microscopy finding suggests acute tubular necrosis?
Muddy brown granular casts on urine microscopy suggest acute tubular necrosis in a child with acute kidney injury. Red cell casts point instead to glomerulonephritis, and white cells with eosinophils suggest interstitial nephritis.
What are the indications for urgent dialysis in paediatric acute kidney injury?
Urgent dialysis in paediatric acute kidney injury is indicated for refractory hyperkalaemia, severe metabolic acidosis, and fluid overload with respiratory compromise. Uraemic pericarditis, encephalopathy and severe drug toxicity are also indications.
Does acute kidney injury in childhood increase the risk of chronic kidney disease later?
Acute kidney injury in childhood does increase the later risk of chronic kidney disease, particularly after severe or repeated episodes. Children who recover should have periodic review of blood pressure, urine protein and creatinine.