Normal Urine Output in Adults
For adults with normal renal function not receiving diuretics, normal urine output is at least 0.8-1.0 liters per 24 hours, which translates to approximately 0.5 mL/kg/hour or higher. 1
Standard Thresholds
The normal urine output parameters are well-established across multiple guidelines:
- Minimum acceptable output: ≥0.5 mL/kg/hour in adults 1, 2
- Daily volume equivalent: For a 70 kg patient, this equals approximately 840 mL/day (0.5 mL/kg/h × 70 kg × 24 hours) 1
- Practical target: Patients with symptoms are typically advised to aim for 1 liter per 24 hours 3
Clinical Context for Oliguria
Understanding what constitutes abnormally low output helps define the normal range:
- Oliguria threshold: <0.5 mL/kg/hour sustained for at least 6 hours 2, 4
- Traditional oliguria definition: <400 mL per day total urine output 2, 4
- Anuria: <100 mL per 24 hours 4
Recent research suggests the current oliguria definition may be too liberal, with a 6-hour threshold of 0.3 mL/kg/hour showing stronger association with mortality and dialysis need 5. However, the 0.5 mL/kg/hour threshold remains the guideline standard 1, 2.
Polyuria Assessment
When evaluating excessive urine output:
- 24-hour polyuria: Defined as >3 liters total output 3
- Nocturnal polyuria: >33% of 24-hour urine output occurring at night 3, 4
Important Clinical Considerations
Measurement method matters: The average method of assessing urine output (mean UO below threshold) identifies oliguria in 73% of ICU patients, while the persistent method (all measurements below threshold) identifies it in only 54% 6. Both methods show similar mortality associations after adjustment, but this highlights the importance of standardized definitions 6.
Weight-based calculations: The standard formula of mL/kg/hour becomes problematic in obese patients due to nonlinear relationships between body weight and expected urine output 2. Consider using adjusted body weight in this population 2.
Diuretic effects: Urine output thresholds become unreliable in patients receiving diuretics, as these medications artificially increase output without improving kidney function 2.