Synopsis
Quantify abnormal urine output, distinguish filtration failure, obstruction, water diuresis, solute diuresis and nocturnal bladder symptoms, and prevent sodium or volume emergencies.
- Measure output before labelling it. In adults, NICE AKI recognition uses oliguria below 0.5 mL/kg/hour; catheter patency, collection errors and actual body weight must be checked.
- Anuria is particularly concerning for complete obstruction, catheter blockage, severe shock, vascular catastrophe or advanced intrinsic failure and warrants immediate reassessment.
- Oliguria is a functional signal that can precede creatinine rise. It does not prove hypovolaemia, and a fluid bolus can worsen heart failure or renal venous congestion.
Key red flags
Output below the weight-adjusted threshold with acute illness, creatinine rise, hypotension, congestion or nephrotoxin exposure requires rapid cause and complication assessment. Oliguria can exist without a catheter if measurement is reliable.
Investigation priorities
Confirm oliguria, anuria or true polyuria and establish severity.
Management branches
Output below 0.5 mL/kg/hour, no urine or an unexpected sharp decline.
- Confirm measurement and catheter patency, perform ABCDE, assess depletion versus congestion and obtain urgent potassium, creatinine, bicarbonate and ECG where indicated.
- Use bladder scanning and urgent ultrasound when obstruction is possible; involve urology immediately for infected obstruction, solitary-kidney blockage or unrelieved retention.
Key medicines
Desmopressin for established AVP deficiencyContinue the patient's prescribed route and dose; decompensation requires specialist fluid-first management and carefully monitored parenteral dosing rather than automatic substitution.
Diuretic timing reviewKeep the clinically indicated total dose unless the prescriber changes it; move timing earlier only after reviewing congestion, blood pressure, renal function and daily routine.