What is the normal range of Urine Output (UOP)?

Normal Range of Urine Output (UOP)

Normal urine output in adults is ≥0.5 mL/kg/hour, which translates to approximately 0.8-1.0 L per day (or roughly 35 mL/hour in a 70 kg patient). 1, 2

Standard Thresholds by Population

• Adults and children: Normal UOP is ≥0.5 mL/kg/hour 1
• Neonates: Require higher thresholds of >1.0 mL/kg/hour 1
• Daily total: For patients with normal renal function not receiving diuretics, expect at least 0.8-1.0 L per day 2

Clinical Context: When Urine Output Becomes Abnormal

Oliguria Definitions

• Standard oliguria: <0.5 mL/kg/hour sustained for at least 6 hours 1, 3
• Traditional daily threshold: <400 mL/day (equivalent to 0.24 mL/kg/h in a 70-kg patient) 1
• Pediatric oliguria: <0.5 mL/kg/hour for 8 hours 4

Anuria Definitions

• Adults: <100 mL per 24 hours 3
• Pediatrics: <0.3 mL/kg/hour for 24 hours or 0 mL/kg/hour for 12 hours 4, 1

Emerging Evidence on Optimal Thresholds

Recent research challenges the traditional 0.5 mL/kg/hour threshold. A 2025 multicenter study found that urine output >1.0 mL/kg/hour on the day of sepsis diagnosis was associated with lower AKI incidence, with cubic spline analysis suggesting thresholds of 1.2-1.3 mL/kg/hour for AKI prediction. 5 This suggests that what we consider "normal" may actually represent a spectrum, with higher outputs conferring better outcomes.

Additionally, a 2013 study demonstrated that a 6-hour threshold of 0.3 mL/kg/hour (rather than 0.5 mL/kg/hour) was independently predictive of hospital mortality and 1-year mortality, suggesting the current AKI definitions may be too liberal. 6

Practical Calculation for Bedside Use

For a standard 70 kg adult:

• Minimum acceptable: 0.5 mL/kg/h × 70 kg = 35 mL/hour or 840 mL/day 2
• Optimal target during fluid resuscitation: >0.5 mL/kg/hour 2

Critical Pitfalls to Avoid

• Diuretic use invalidates thresholds: Diuretics artificially increase output without improving kidney function, making UOP unreliable for assessing renal status 4, 1, 2
• Obesity complicates calculations: The weight-based definition becomes problematic in obese patients due to nonlinear relationships between body weight and expected urine output; consider using adjusted body weight 1
• Cirrhotic patients with ascites: UOP is often unreliable due to avid sodium retention despite relatively normal GFR 1, 2
• Single void volume ≠ hourly rate: Do not confuse individual void volumes with hourly output rates—these measure different physiologic parameters 3

Measurement Method Matters

The method used to assess oliguria has major diagnostic implications. A 2024 observational study found that using an average UOP method (mean UOP below threshold) identified oliguria in 73% of patients versus 54% using a persistent method (all measurements below threshold), with the average method showing higher sensitivity but lower specificity for mortality prediction. 7 This highlights the need for standardization in clinical practice.