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Nephrology

Acute Kidney Injury

Abrupt kidney function loss over hours to days defined by KDIGO creatinine or urine output criteria; classified as pre-renal, intrinsic, or post-renal.

Last reviewed 30 May 2026 - MedicoMedics editorial team

Acute kidney injury nephron ischaemia

Pathophysiology

Pre-renal: volume depletion, heart failure, hepatorenal, sepsis. Intrinsic: ATN (ischaemia, nephrotoxins), AIN (drugs), glomerular, vascular. Post-renal: obstruction.

Sources: KDIGO AKI (Kidney Int Suppl 2012;2:1); NEJM AKI 2017;377:1064

Presentation

Oliguria (<0.5 mL/kg/h), rising creatinine, volume overload, hyperkalaemia, metabolic acidosis; uraemic symptoms if severe.

Diagnosis

KDIGO: creatinine rise >=0.3 mg/dL in 48 h, or >=1.5x baseline in 7 days, or urine output <0.5 mL/kg/h for 6 h. Urinalysis, FeNa, ultrasound to localise cause.

Management

Correct volume, treat cause, hold nephrotoxins (NSAIDs, aminoglycosides, contrast). Absolute indications for RRT: refractory hyperkalaemia, acidosis, volume overload, uraemic pericarditis/encephalopathy, dialyzable toxins (AEIOU).

Sample USMLE-style MCQs

Try 5 questions on this topic. Practice hundreds more free with a trial.

Question 1

Elderly patient on ibuprofen and lisinopril develops AKI after vomiting. Muddy brown casts. Diagnosis?

Question 2

Which is an indication for urgent dialysis?

Question 3

Best test to differentiate pre-renal from ATN in a patient on furosemide?

Question 4

Which drug can cause AIN with eosinophiluria?

Question 5

Post-renal AKI first step?

References

Primary guidelines and peer-reviewed sources used for this entry. Reviewed 30 May 2026 by MedicoMedics editorial team.

  1. KDIGO AKI (Kidney Int Suppl 2012;2:1)
  2. NEJM AKI 2017;377:1064

Frequently asked

What FeNa suggests pre-renal?

<1% (except with diuretics; use FeUrea <35% instead).

Classic urine finding in ATN?

Muddy brown granular casts.

Contrast nephropathy risk factor?

CKD, diabetes, volume depletion - prevent with hydration.

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