Normal Daily Urine Output
Healthy adults normally generate approximately 1-2 liters of urine per day. 1
Standard Volume Range
- Normal daily urine output ranges from 1,000 to 2,000 mL (1-2 liters) per 24 hours in healthy adults 1
- This volume is produced by the kidneys to eliminate waste products (urea, metabolites) and maintain homeostasis of water, ions, and pH in blood 1
- For patients with normal renal function who are not receiving diuretics, urine output should be at least 0.8-1 L per day 2
Hourly Rate Equivalents
When expressed as an hourly rate, normal urine output translates to:
- ≥0.5 mL/kg/hour is the standard threshold for adequate urine output in adults 1, 2
- For a 70 kg patient, this equals approximately 35 mL/hour or 840 mL/day 2
- Some evidence suggests that urine output >1.0 mL/kg/hour may be associated with lower rates of acute kidney injury in critically ill patients 3
Factors Affecting Urine Volume
Urinary concentration and volume are highly variable due to several physiological factors 1:
- Fluid intake (water loading can increase output to 5-6 liters/day) 4
- Time of collection 1
- Diet and exercise 1
- Age and gender 1
- Medications 1
- Health status 1
Research demonstrates that during water restriction, urine volume can fall to less than 1 liter per 24 hours (as low as 0.77 L/day), while water loading can increase output to approximately 6 liters per 24 hours 4
Clinical Thresholds for Concern
Oliguria is defined as urine output <0.5 mL/kg/hour for at least 6 hours 1, 5, which represents a clinically significant reduction requiring evaluation:
- Traditional oliguria threshold: <400 mL/day (equivalent to 0.24 mL/kg/h in a 70-kg patient) 5
- Urine output <1 L per 24 hours is considered a clinical warning sign requiring attention to determine if low flow is due to inadequate water intake or disease-induced dehydration 6
Common Pitfalls
- Do not rely solely on urine output in patients receiving diuretics, as these medications artificially increase output without necessarily reflecting kidney function 1, 5
- In cirrhotic patients with ascites, urine output may be low despite relatively normal kidney function due to avid sodium retention 1, 2
- Weight-based calculations become problematic in obese patients due to the nonlinear relationship between body weight and expected urine output 5