What is the normal urine output in milliliters per kilogram per hour for a healthy adult with normal renal function?

Normal Urine Output in Adults

Normal urine output in healthy adults with normal renal function is ≥0.5 mL/kg/hour, which translates to approximately 840 mL/day for a 70 kg patient, or a minimum of 0.8-1.0 liters per 24 hours. 1

Standard Thresholds

• The American College of Physicians establishes a minimum acceptable urine output of ≥0.5 mL/kg/hour in adults 1
• For a 70 kg patient, this equals approximately 35 mL/hour or 840 mL/day 2
• Patients with symptoms are typically advised to aim for 1 liter per 24 hours 1
• The daily volume equivalent is at least 0.8-1.0 liters per 24 hours 1

Clinical Context and Abnormal Values

Oliguria Definition

• Oliguria is defined as urine output <0.5 mL/kg/hour sustained for at least 6 hours, with a traditional definition of <400 mL per day total urine output 1, 3
• This threshold is incorporated into KDIGO, RIFLE, and AKIN classification systems for acute kidney injury diagnosis 3

Anuria Definition

• Anuria is defined as urine output <100 mL per 24 hours 1
• Alternatively, anuria can be defined as <0.3 mL/kg/hour for 24 hours or complete absence (0 mL/kg/hour) for ≥12 hours 3

Polyuria Definition

• 24-hour polyuria is defined as >3 liters total output 1
• Nocturnal polyuria is defined as >33% of 24-hour urine output occurring at night 1

Acute Kidney Injury Staging by Urine Output

The KDIGO criteria establish severity gradients based on duration and degree of reduced urine output:

• Stage 1 AKI: <0.5 mL/kg/hour for 6-12 hours 2, 3
• Stage 2 AKI: <0.5 mL/kg/hour for ≥12 hours 2, 3
• Stage 3 AKI: <0.3 mL/kg/hour for ≥24 hours OR anuria for ≥12 hours 2, 3

Important Clinical Caveats

Obese Patients

• The standard formula of mL/kg/hour becomes problematic in obese patients due to nonlinear relationships between body weight and expected urine output 1, 3
• Adjusted body weight should be considered for calculations in this population 1, 3

Patients Receiving Diuretics

• Urine output thresholds become unreliable in patients receiving diuretics, as these medications artificially increase output without improving kidney function 1, 2
• Diuretic administration can change oliguria classification without changing actual renal function 3

Cirrhotic Patients with Ascites

• In patients with cirrhosis and ascites, urine output is an unreliable marker of renal function because these individuals often exhibit oliguria with avid sodium retention despite potentially normal glomerular filtration rate 4, 2
• Diuretic therapy may artificially increase urine volume without reflecting true kidney recovery 4, 2
• Accurate urine collection is frequently difficult in this population 4

Volume Status Considerations

• Oliguria may represent an appropriate physiologic response to volume depletion rather than intrinsic kidney injury 3
• The duration of oliguria is more clinically significant than whether the patient is receiving IV fluids 3
• Oliguria persisting despite adequate fluid resuscitation suggests intrinsic kidney injury or inadequate perfusion pressure, with significantly worse prognosis 3

Critical Action Thresholds

• A urine output of <4 mL/kg over 8 hours is an absolute indication to suspend nephrotoxic therapies 2, 3
• Persistent oliguria (<0.5 mL/kg/hour) despite adequate fluid boluses indicates the need to reevaluate the management strategy 2