Acute Kidney Injury (AKI): KDIGO Criteria and Management

Acute kidney injury (AKI) is a sudden fall in kidney function over hours to days. It is common in hospital patients, especially the elderly and acutely unwell. AKI is often preventable, and early recognition can stop it progressing to dialysis or death.

Definition (KDIGO)

Any one of:

• A rise in serum creatinine of 26.5 µmol/L (0.3 mg/dL) or more within 48 hours.
• A rise in creatinine to 1.5 times baseline or more, known or presumed to have occurred within the previous 7 days.
• Urine output below 0.5 mL/kg/hour for 6 hours or more.

AKI is staged 1 to 3 by the size of the creatinine rise and the fall in urine output.

Causes

• Pre-renal (reduced blood flow to the kidneys; the most common):
  • dehydration
  • bleeding
  • sepsis
  • heart failure
  • liver failure
  • drugs that reduce kidney perfusion
• Renal (intrinsic):
  • acute tubular necrosis from prolonged hypoperfusion or toxins (aminoglycosides, contrast, myoglobin in rhabdomyolysis)
  • acute interstitial nephritis (often drug-induced, for example PPIs, NSAIDs and antibiotics)
  • glomerulonephritis
  • vascular causes
• Post-renal (obstruction):
  • enlarged prostate
  • stones
  • tumours
  • a blocked catheter

Risk factors

• Age over 65.
• Chronic kidney disease.
• Diabetes.
• Heart failure.
• Liver disease.
• Sepsis.
• Hypovolaemia.
• Nephrotoxic drugs.
• Iodinated contrast.
• Major surgery.

Assessment

• Fluid status and blood pressure; review the drug chart.
• Urine dipstick: blood and protein suggest glomerulonephritis.
• Blood tests: urea, creatinine and electrolytes, especially potassium; full blood count; bicarbonate or venous blood gas; creatine kinase if rhabdomyolysis is possible.
• Renal tract ultrasound within 24 hours if obstruction is suspected or the cause is unclear.
• Further tests if glomerulonephritis is possible: autoantibodies, complement and urine protein:creatinine ratio.

Management

• Treat the cause: fluids for hypovolaemia, antibiotics for sepsis, relieve obstruction (catheter, nephrostomy).
• Stop or hold nephrotoxic and risky drugs:
  • NSAIDs
  • ACE inhibitors and ARBs
  • diuretics
  • metformin
  • aminoglycosides
  Adjust other drug doses for kidney function.
• Monitor fluid balance, daily weights, urine output and electrolytes closely.
• Treat complications, especially hyperkalaemia:
  • IV calcium to protect the heart
  • insulin with glucose and nebulised salbutamol to shift potassium into cells
  • then remove potassium from the body
• Refer to nephrology for suspected glomerulonephritis, AKI stage 3, or complications.

Indications for urgent dialysis

Remember "AEIOU":

• Acidosis — severe, refractory.
• Electrolytes — refractory hyperkalaemia.
• Intoxication — dialysable toxins.
• Overload — fluid overload not responding to diuretics.
• Uraemia — complications such as pericarditis or encephalopathy.

Exam pearls

• Always consider obstruction. A bladder scan or ultrasound is quick and can be life-saving.
• Hyperkalaemia with ECG changes (peaked T waves, broad QRS) needs IV calcium immediately.
• Blood and protein on urine dipstick with AKI: think glomerulonephritis and refer urgently.

See also Chronic Kidney Disease, Sepsis and the nephrology part of our Medicine Companion.

Test yourself

5 exam-style single-best-answer questions. Choose your answer, then tap “Show answer”.

1. Which meets the KDIGO definition of AKI?

   1. eGFR 70 for 6 months
   2. Creatinine rise of 26.5 µmol/L or more within 48 hours
   3. Proteinuria alone
   4. Creatinine rise of 10 µmol/L in 48 hours
   5. Urine output 1 mL/kg/h
   Show answer

   Answer: B. Creatinine rise of 26.5 µmol/L or more within 48 hours
   AKI: creatinine rise ≥26.5 µmol/L in 48 h, ≥1.5× baseline within 7 days, or urine <0.5 mL/kg/h for 6 h.

2. Potassium 7.1 mmol/L with peaked T waves and broad QRS. First drug?

   1. IV calcium gluconate or chloride
   2. Sodium bicarbonate only
   3. Salbutamol only
   4. Furosemide
   5. Oral calcium resonium only
   Show answer

   Answer: A. IV calcium gluconate or chloride
   IV calcium stabilises the myocardium immediately; then shift and remove potassium.

3. An elderly man with AKI and a palpable bladder. Likely cause?

   1. Pre-renal
   2. Interstitial nephritis
   3. Post-renal obstruction
   4. Acute tubular necrosis
   5. Glomerulonephritis
   Show answer

   Answer: C. Post-renal obstruction
   Urinary retention (e.g. prostatic enlargement) causes post-renal AKI; catheterise.

4. Which drug should usually be withheld in AKI?

   1. Paracetamol
   2. Insulin
   3. Thiamine
   4. Omeprazole
   5. NSAIDs
   Show answer

   Answer: E. NSAIDs
   NSAIDs, ACE inhibitors/ARBs, diuretics, metformin and aminoglycosides are reviewed or held.

5. Which is an indication for urgent dialysis?

   1. Urine output 1 mL/kg/h
   2. Creatinine 150
   3. Refractory hyperkalaemia
   4. Mild acidosis
   5. Normal potassium
   Show answer

   Answer: C. Refractory hyperkalaemia
   AEIOU: refractory Acidosis, Electrolytes (K), Intoxication, Overload, Uraemic complications.

More articles in Nephrology & Urology

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• Kidney Stones and Renal Colic: Diagnosis and TreatmentTypes of stones, risk factors, renal colic, CT KUB, pain relief, which stones pass, ESWL, ureteroscopy, emergency drainage and prevention.

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Disclaimer

For education and exam preparation only. This is not medical advice and must not be used to diagnose or treat patients. Always follow current clinical guidelines and the advice of qualified senior colleagues.