Acute Kidney Injury

Overview Acute kidney injury (AKI) is the syndrome arising from a rapid fall in GFR (over hours to days). It is characterised by retention of both nitrogenous (including Urea and Creatinine) and non-nitrogenous waste products of metabolism, as well as disordered electrolyte, acid–base, and fluid homeostasis.

Remember AKI is neither a diagnosis nor a disease. Rather, it is a clinical syndrome that is caused by, or complicates, a wide range of disorders
Acute Kidney Injury: Rapid reduction in kidney function over hours to days, as measured by serum urea and creatinine and leading to a failure to maintain fluid, electrolyte and acid-base homeostasis.
Chronic Kidney Disease: Impaired renal function >3months based on abnormal structure or function, or GFR <60 for >3months.
Oliguria: A urine output of <400ml/day may be the earlier sign of impaired renal function

Classification The aetiology of acute kidney injury can be simply divided into pre-renal, renal and post renal causes.

  • Pre-renal - Sepsis and hypotension
    • Severe sepsis
    • Haemorrhage
    • Dehydration
    • Cardiac failure
    • Liver failure
    • Renovascular insult
  • Intrarenal
    • Toxicity
      • Nephrotoxic drugs
      • Iodinated radiological contrast
    • Parenchymal kidney disease
      • Glomerulonephritis
      • Tubulointerstitial nephritis
      • Rhabdomyolysis
      • Haemolytic uraemic syndrome
      • Myeloma
      • Malignant hypertension
  • Post renal Obstruction
    • Bladder outflow
    • Stones
    • Tumour
    • Surgical ligation of ureters
    • Extrinsic compression (lymph nodes)
    • Retroperitoneal fibrosis

Approach to Acute Kidney Injury


  • Prerenal causes
    • Vomiting, diarrhoea, polyuria
    • Use of diuretics
    • Dehydration
    • Assess for comorbidities which may reduce renal perfusion - heart failure, shock
  • Renal causes
    • Diuretics and other nephrotoxins (NSAIDs, ARBs, ACEI)
    • Palpable purpura, pulmonary haemorrhage or sinusitis raises suspicion of systemic vasculitis with glomerulonepritis
    • Polyarthralgia, rash suggests rheumatological cause such as SLE
    • Recent injury, limb ischaemia suggest rhabdomyalsis
    • Fevers night sweat and chills may suggest vasculitis or urine infection
  • Postrenal obstruction
    • Nocturia, hesitancy and urgency suggest prostate issues
    • Severe flank pain with history of stones suggest nephrolithiasis
    • Suprapubic discomfort may suggest urinary retention
  • Other questions
    • Haematuria


  • Stable or unstable patient
  • Vitals signs
  • Catheter in situ? - Haematuria
  • Urine output chart
  • Assess fluid status - hypovolaemia, normovolemic or hypervolaemic
    • Hypovolaemic - reduced skin turgor, dry mucus membranes
    • Hypervolaemic - JVP elevated, peripheral oedema, pulmonary coarse inspiratory crackles (pulmonary oedema)

Bedside test

  • Urine analysis
  • Urine sediment examination and microscopy
    • Urine that has been centrifuged to concentrate the substances in it at the bottom of a tube

Drawing for urine sediment examination....


  • FBC
  • EUC
  • LFT
  • CMP
  • Urine casts
  • Urine albumin/creatinine ratio
  • Urine protein/creatinine ratio