Normal Urine Output Per Hour
Normal urine output in adults is 0.5-1.0 mL/kg/hour, with less than 0.5 mL/kg/hour for more than 6 hours considered oliguria and potentially indicating acute kidney injury. 1
Standard Urine Output Parameters
Adult Parameters
- Normal range: 0.5-1.0 mL/kg/hour
- Daily volume: Approximately 0.8-1.0 L/day for patients with normal renal function 1
- Oliguria threshold: <0.5 mL/kg/hour for >6 hours 1
- Anuria threshold: <0.3 mL/kg/hour for 24 hours or complete absence of urine for 12 hours 1
Pediatric Parameters
- Neonates: Oliguria defined as <0.5-1.0 mL/kg/hour for longer than 12 hours 1
Clinical Significance of Urine Output Measurements
Acute Kidney Injury Staging Based on Urine Output
- Stage 1: <0.5 mL/kg/hour for 6-12 hours 1
- Stage 2: <0.5 mL/kg/hour for ≥12 hours 1
- Stage 3: <0.3 mL/kg/hour for ≥24 hours or anuria for ≥12 hours 1
Emerging Research on Urine Output Thresholds
Recent research suggests that the standard 0.5 mL/kg/hour threshold may be too liberal:
- A study found that a 6-hour urine output threshold of 0.3 mL/kg/hour was better associated with mortality and dialysis need 2
- Another study indicated that urine output >1.0 mL/kg/hour was associated with lower AKI incidence in sepsis patients 3
Measurement Considerations
Calculation Methods
- Average method: Mean urine output below threshold over a time period
- Persistent method: All measurements below threshold over a time period
- The average method identifies oliguria more frequently (73% vs 54.3%) but has lower specificity 4
Body Weight Considerations
- Using actual body weight (ABW) rather than ideal body weight (IBW) in obese patients may lead to overestimation of AKI 5
- Consider using ideal body weight for more accurate assessment in obese patients
Clinical Monitoring and Intervention
- Oliguria (<0.5 mL/kg/hour) persisting for >6 hours requires clinical attention 1
- Anuria (<100 mL/24 hours) requires immediate intervention 1
- Assessment and correction of fluid status is essential, with consideration of fluid challenge if oliguria persists 1
Common Pitfalls to Avoid
- Failing to account for body weight: Urine output should be calculated based on patient weight, not just absolute volume
- Using inappropriate weight metrics: Consider using ideal body weight in obese patients
- Ignoring collection method: Ensure accurate measurement through proper catheterization when precise measurements are needed
- Not considering medication effects: Diuretics and other medications can significantly alter urine output
- Overlooking hydration status: Interpret urine output in context of the patient's fluid status and intake