There are various definitions:

Oliguria can generally be defined as <0.5ml/kg/hour or <300ml per day (whether catheterised or not).

Anuria <50ml/day.  Anuria is an emergency requiring rapid management.


  • Urine volume is a difference of the amount of fluid filtered by the glomerulus and that reabsorbed by the renal tubules
    • It is not (directly) a measure of renal function (reduced GFR and reduced tubule reabsorption -> normal urine volume)
    • HOWEVER, it is commonly used as a physical measure of renal function in the acute setting, as reduced urine output is often one of the first physiological signs of hypovolaemia and/or shock
  • Can be a result of reduced urine production
    • Acute kidney injury e.g. pre-renal AKI in diabetic ketoacidosis, dehydration or blood loss; or intra-renal AKI e.g. in glomerulonephritis
  • Rarely a result of obstruction
    • Obstruction would have to be complete and below the level of the bladder neck; or bilateral; or unilateral on the side of a single-functioning kidney

Clinical Assessment

  • Commonly, as a doctor you will be asked to review a patient with poor urine output as a sign of patient deterioration (whether this is associated with other physiological changes e.g. heart rate/BP etc or not)
    • ABCDE!
  • THEN a History (if patient is able to give one)
    • Try and determine the timeline (onset; Any history of fluid loss e.g. diarrhoea, vomiting, bleeding, post operative)
    • Ask about PMHx and RHx
      • Stones, kidney problems in the past
      • Drugs e.g. Gentamicin, NSAIDs, ACEIs/ARBs, Antibiotics (and STOP these if renal function/U&Es are deteriorating also)
      • Diarrhoea (particularly E coli O157)
  • Look for signs of hypotension, tachycardia, tachypnoea, fever (any suggestion of sepsis/shock) and fluid depletion 
  • Palpate for bladder distension/tenderness
  • In patients with a catheter, check catheter patency before further investigations, particularly if the patient is normotensive


  • Urinalysis
    • Prerenal causes can have normal urinalysis
    • In intrinsic (AKI cause by ATN)
      • Haematuria/Proteinuria
      • There may be red cell or granular casts
  • FBC and U&Es (particularly sodium, potassium, urea, creatinine (and eGFR)
  • If infection is suspected
    • FBC, CRP
  • ABGs (metabolic acidosis)
  • Kidney USS can be performed
  • Urinary electrolytes can also be measured although this is not routine


  • Any cause of acute kidney injury
    • Prerenal
      • e.g. volume depletion (bleeding, dehydration)
      • e.g. low cardiac output (MI, heart failure, PE)
      • e.g. decreased vascular resistance (shock, sepsis)
    • Renal e.g. acute tubular necrosis, glomerular disease
    • Post-renal e.g. blocked catheter; stone disease, BPH, sphincter dysfunction (anticholinergics, post operative)

Notes on management

  • Treat reversible causes
    • Restore intravascular volume if necessary
  • Monitor fluid balance closely
    • Do not prescribe any potassium as there is a risk of hyperkalaemia
  • Dialysis may be used in patients where
    • Volume expansion that cannot be managed with diuretics
    • Refractory hyperkalaemia
    • Severe uraemia
      • NB No absolute indications- based on clinical judgement (duration, severity etc)

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