Normal Urine Output Per Minute
Normal urine output is approximately 0.5-1.0 mL/kg/hour, which translates to roughly 0.008-0.017 mL/kg/minute for adults. 1
Standard Thresholds by Time Interval
For practical clinical use, urine output is typically measured over longer intervals rather than per minute:
- Per hour: The standard minimum threshold is 0.5 mL/kg/hour for adults, which represents adequate renal perfusion 1, 2, 3
- Per minute calculation: For a 70 kg adult, this equals approximately 0.6 mL/minute (35 mL/hour ÷ 60 minutes) 1
- Daily output: Normal adults should produce at least 0.8-1.0 L per day (approximately 0.6-0.7 mL/minute) 1
Age-Specific Variations
Neonates require significantly higher urine output thresholds than adults due to their physiology:
- Neonates: >1.0 mL/kg/hour (>0.017 mL/kg/minute) is considered normal 2
- Pediatric patients: 80-100 mL/m²/hour during aggressive hydration, or 4-6 mL/kg/hour if <10 kg 3
- Research suggests that neonatal oliguria should be defined as <1.5 mL/kg/hour rather than the adult threshold, as this correlates better with mortality 4
Clinical Context for Oliguria Detection
Oliguria is defined as <0.5 mL/kg/hour sustained over at least 6 hours, which equals <0.008 mL/kg/minute 5, 2. However, the duration of measurement is critical:
- 6 hours at <0.5 mL/kg/hour: Indicates AKI Stage 1 5, 2
- 12 hours at <0.5 mL/kg/hour: Indicates AKI Stage 2 5, 2
- 24 hours at <0.3 mL/kg/hour: Indicates AKI Stage 3 5, 2
Recent research suggests the current 0.5 mL/kg/hour threshold may be too liberal, with a 6-hour threshold of 0.3 mL/kg/hour (0.005 mL/kg/minute) showing stronger association with mortality and dialysis need 6.
Important Clinical Caveats
The per-minute calculation has limited clinical utility because:
- Urine production is not constant minute-to-minute; it varies with hydration status, hormonal influences, and renal perfusion 1
- Measurement intervals of 6 hours or longer are more clinically meaningful for detecting true oliguria versus transient fluctuations 5, 2, 6
- In cirrhotic patients with ascites, urine output criteria become unreliable due to avid sodium retention despite potentially normal GFR 5
For obese patients, use adjusted body weight rather than actual weight, as the weight-based definition becomes problematic due to nonlinear relationships between body weight and expected urine output 2.
Diuretic administration invalidates urine output thresholds for assessing renal function, as it artificially increases output without improving kidney function 5, 2, 3.