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Acute Kidney Injury Part 1:

Classification of the aetiology of Acute Kidney Injury (AKI, Acute Renal Failure )

AKI 1 causes


Table 1: Aetiology of Acute Kidney Injury

Intrinsic (renal)
Obstructive (post-renal)


  • Results from a compromise to renal perfusion and oxygen supply
  • Is commonly due to hypovolaemia or hypotension
  • Can be potentiated by a number of medicines, including non-steroidal agents, ACE inhibitors and angiotensin II antagonists which should be stopped. If there is a strong indication for an ACE inhibitor consider restarting following recovery with close monitoring of renal function.
  • Shock and toxins can result in damage to the renal parenchyma with acute tubular necrosis, therefore pre-renal and intrinsic renal causes of acute kidney injury may co-exist.


  • Usually result from renal artery disease and aortic atheroma/cholesterol emboli.
  • Cholesterol emboli commonly follow intervention e.g. angiography or on commencement of anticoagulation.


Remember: patients with a systemic vasculitis (microscopic polyarteritis, Wegener’s syndrome, SLE) may present with multiple organ failure and mimic sepsis. Have a high index of suspicion: early immunotherapy may save life and functional renal tissue.


  • All mediated through direct damage to the renal parenchyma



  • Acute tubular necrosis

- Ischaemia

- Nephrotoxins:

• Drugs: NSAIDs, aminoglycosides, paracetamol in overdose.
• Poisons: methanol, ethylene glycol.
• Contrast media.

  • Specific conditions

- Vasculitis/glomerulonephritis: is there a history of skin rash, arthralgia/arthritis, rigors?

- Accelerated phase hypertension.

- Interstitial nephritis: follows a period of drug exposure in most instances.

- Infections: legionella, leptospirosis, malaria.


  • Results from blockage to urinary flow.
  • This implies that both ureters are blocked or that outflow from a single functioning kidney has been impeded.



  • Renal tubules/pelvis, ureters with myoglobinuria, haemoglobinuria, crystal formation eg uric acid in tumour lysis syndrome, myeloma and papillary sloughing (e.g. diabetes).
  • Ureteric/urethral as in prostatic hypertrophy or bladder/ureter blockage as a result of tumour, stone, clot or stricture.

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