Medically Fit For Exams
Medically Fit For Exams

Acute Kidney Injury (AKI)


  • Rapid onset failure of the kidneys, NICE define by any of the following
    • Rise in serum creatinine >26micromol/L in 48 hours
    • 50% rise in creatinine known (or suspected) to be within last 7 days
    • Fall in urine output to < 0.5ml/kg/hour for over 6 hours in adults, 8 hours in children
    • >25% fall in eGFR in children and young people in last 7 days


Risk factors

  • Chronic kidney disease
  • Heart failure
  • Liver disease
  • Diabetes
  • Reduced fluid intake (maybe as a result of neurological or cognitive problems)
  • Volume loss from vomiting/diarrhoea
  • Hypotension/hypovolemia
  • Use of nephrotoxic drugs
    • NSAIDs
    • ACE inhibitors
    • Angiotensin 2 receptor inhibitors
    • Iodinated contrast medium (CT)
  • History of AKI
  • History of renal/urinary obstruction
  • Trauma (rhabdomyolysis)
  • Sepsis
  • Age over 65


Differential diagnoses

  • Chronic kidney disease
  • Urinary retention
  • Bladder cancer
  • Kidney cancer
  • Urinary obstruction



  • About 15% of adults admitted to hospital develop AKI
  • Estimated cost of hospital-AKI is £630 million per year to the NHS
  • Especially common in the elderly, as kidney function slowly declines with age



  • Pre renal – anything causing reduced perfusion
    • Hypovolemia
    • Hypotension
    • Shock
    • Heart failure
    • Renal stenosis
  • Intra-renal – anything affecting the kidney itself
    • Acute tubular necrosis
      • Ischemia (any pre-renal cause)
      • Damage by nephrotoxic drugs (NSAIDS, ACEIs, contrast)
      • Rhabdomyolysis (muscle break down – myoglobin is toxic)
      • Sepsis – lipopolysaccharides of gram-negative bacteria are toxic
    • Glomerular disease
    • Acute interstitial nephritis (from drugs, infection, hypercalcaemia, myeloma)
    • Vascular disease
      • Malignant/accelerated hypertension
      • Vasculitis
      • Thrombotic microangiopathies
    • Cholesterol embolism
    • Haemolytic uremic syndrome
      • Mostly affects children
      • Haemolysis (breakdown of RBCs)
      • Uremia (high urea)
      • Thrombocytopenia (low WBCs)
    • Thrombotic thrombocytopenic purpura
      • Multiple blood clots in small vessel cause rash-like appearance
      • Disease of coagulation
    • Pre-eclampsia
    • Obstruction of renal tubules
    • Pyelonephritis – usually result of infection
  • Post-renal – anything affecting ureters, bladder, urethra
    • Bladder outflow obstruction
    • Tumour
    • Bilateral stones in ureter (must be bilateral to cause failure, other one can compensate)
    • Retroperitoneal fibrosis – causing ureteral obstruction


Clinical features

  • Similar to chronic kidney failure, but over a shorter period of time
  • Fatigue
  • Anorexia
  • Nocturia (better perfusion to kidneys at night, so more output)
  • Oliguria
  • Symptoms relate to the cause of the kidney failure
    • Hypovolemia: Dizziness, confusion, orthostatic hypotension
    • Infection: Fever, pain, inflammation
    • Heart failure: raised JVP, SOB
  • Hypertension in AKI suggests:
    • Vasculitis
    • Glomerulonephritis
    • Renovascular disease
    • Atheroembolic disease



  • Acute tubular necrosis
    • Tubular cell damage and death
    • Cells most likely to be affected are the straight portion of proximal tubule and thick ascending limb of loop of Henle
    • Cells lose brush border membrane formation of apical bleds
    • Loss of integrity of tight intracellular junctions
    • Loss of epithelial cell barrier, causing back-leak
    • Sloughing of live and dead cells – causing obstruction
    • Necrosis/ischemia/infarction leads to reduction in normal cell products such as NO that act as vasodilators, worsening the obstruction and ischemia
    • Maintenance phase is usually 1-2 weeks
    • Followed by spontaneous recovery phase



  • eGFR
    • Estimates glomerular filtration rate based on age, sex, creatine levels, weight (Cockcroft-Gault equation)
  • Urea:creatinine ratio
    • Creatinine measured in μmol/L, urea measured in mmol/L
    • Ratio of >100:1 (U:C) is indicative of pre-renal cause
    • Ratio of <40:1 is indicative of intra-renal cause
    • Ratio between 40:1 and 100:1 is normal (post-renal cause will also fall in this range
    • The ratio is not diagnostic
  • Creatinine clearance
    • Volume of blood cleared of creatinine per unit time
    • Useful analogue of GFR
    • Usually overestimates GFR slightly
  • Inulin clearance
    • Better analogue of GFR than creatinine clearance
    • Requires infusion of inulin, and concentration in blood or urine can be used to calculate clearance rate
  • Urinalysis
    • Protein and/or blood in the urine is indicative of kidney injury



  • Stop nephrotoxic drugs
  • Monitor creatinine, potassium, sodium, phosphate, calcium, glucose
  • Identify and treat infection
  • Treat the cause
  • Measure and maintain fluid balance
    • General rule: put in what they are putting out
    • Use diuretics in cases of fluid overload (although haven’t been shown to improve outcomes)
  • Dietary restriction
    • Reduced potassium and sodium
  • Dialysis may be necessary
  • Identify and treat complications
    • Hyperkalemia
    • Acidosis
    • Pulmonary oedema
    • Bleeding



  • Majority of cases will resolve once the cause of the injury is treated/removed
  • Depends on co-morbidities, underlying CKD, age etc
Acute kidney injury.docx
Microsoft Word document [16.6 KB]

Get social with us.

Print Print | Sitemap