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Urine Output and AKI Staging

Weight-normalized urine output (mL/kg/hr) is a key KDIGO criterion for acute kidney injury. Normal is ≥0.5 mL/kg/hr.

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Normal ≥0.5 mL/kg/hr Stage 1: <0.5 for 6-12h Stage 2/3: <0.5 for >12h or anuria

Ready to run the numbers?

Why: Urine output detects kidney stress before creatinine rises. Critical for ICU and post-operative monitoring.

How: Volume ÷ time = mL/hr; then ÷ weight = mL/kg/hr. Compare to KDIGO thresholds for staging.

Normal ≥0.5 mL/kg/hrStage 1: <0.5 for 6-12h
Sources:KDIGO GuidelinesUpToDate - Oliguria

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Urine Output Measurement

Total urine during measurement period
mL
Duration of collection
hours
For weight-based calculations
kg

Patient & Context

Patient age
years
Reference range adjustments
Affects interpretation
Altered fluid dynamics
For fluid balance
mL
Affects interpretation

For informational purposes only — not medical advice. Consult a healthcare professional before acting on results.

🏥 Health Facts

💧

— KDIGO 2012

⚠️

— Critical care

📋 Key Takeaways

  • • Normal urine output is ≥0.5 mL/kg/hr (KDIGO criteria)
  • • Oliguria (<0.5 mL/kg/hr for 6+ hours) suggests early AKI
  • • Anuria is a medical emergency requiring immediate intervention
  • • Weight normalization allows comparison across patient sizes
  • • Diuretics can mask oliguria—serum creatinine trends matter

💡 Did You Know?

💧KDIGO Stage 1: &lt;0.5 mL/kg/hr for 6-12 hoursSource: KDIGO 2012
⚠️KDIGO Stage 2: &lt;0.5 mL/kg/hr for &gt;12 hoursSource: KDIGO 2012
🚨KDIGO Stage 3: &lt;0.3 mL/kg/hr or anuria ≥12hSource: KDIGO 2012
🏥Urine output detects shock before creatinine risesSource: Critical care
📊100 kg patient needs more output than 50 kgSource: Physiology
💊Diuretics increase output despite kidney injurySource: Nephrology

📖 How It Works

Converts volume measurements into clinically meaningful rates and compares against KDIGO AKI criteria.

Step 1: Data Collection

Record total urine volume over measured time. Accuracy depends on complete collection.

Step 2: Rate Calculation

Volume ÷ time = mL/hr; then ÷ weight = mL/kg/hr for comparison across patients.

Step 3: KDIGO Classification

Compare to thresholds: Normal ≥0.5; Stage 1 <0.5 for 6-12h; Stage 2 <0.5 for >12h; Stage 3 <0.3 or anuria.

🎯 Expert Tips

Accurate Measurement

Use Foley for continuous measurement in critically ill patients.

Document Timing

Exact start and end times of collection are critical.

Diuretic Caveat

Diuretics increase output despite injury. Serum creatinine trends matter.

Red Flags

Anuria, rapid decline, no response to fluids—urgent intervention.

⚖️ This Tool vs Manual

FeatureThis CalculatorManual
mL/kg/hr calculation✅❌
KDIGO AKI staging✅❌
Fluid balance estimate✅❌
Visual charts✅❌

❓ FAQ

What is normal urine output?

≥0.5 mL/kg/hr, roughly 30-50 mL/hr or 800-2000 mL/24h for adults.

Why normalize by weight?

Larger patients need more output to eliminate waste per kg of tissue.

What causes decreased urine output?

Prerenal (dehydration, heart failure), intrinsic renal (ATN, nephrotoxins), or postrenal (obstruction).

Does diuretic use affect AKI staging?

Yes. Diuretics can increase output despite injury. Serum creatinine trends become more important.

When to be concerned about oliguria?

&lt;0.5 mL/kg/hr for 6+ hours. Immediate concern for anuria, hypotension, sepsis.

📊 KDIGO Urine Output Criteria

≥0.5
Normal
<0.5
Stage 1 (6-12h)
<0.5
Stage 2 (>12h)
<0.3
Stage 3 / Anuria

⚠️ Disclaimer: This calculator is for educational purposes only. Urine output interpretation requires clinical context. Always consult a qualified healthcare provider.

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