Kidney Stone Calculator
STONE scoring system for percutaneous nephrolithotomy success prediction
STONE Scoring Parameters
Calculated as stone length × width on CT scan. Points: 0-399 mm² (0 pts), 400-799 mm² (1 pt), 800-1599 mm² (2 pts), ≥1600 mm² (3 pts)
Distance from stone center to skin on CT. Points: ≤100 mm (0 pts), >100 mm (1 pt)
Presence and severity of hydronephrosis. Points: No/mild (0 pts), Moderate/severe (1 pt)
Number of kidney calyces containing stones. Points: 1-2 (0 pts), 3 (1 pt), Staghorn (2 pts)
Stone density measured in Hounsfield units (HU) on CT. Points: ≤950 HU (0 pts), >950 HU (1 pt)
STONE Score Results
Excellent success rate
Score Breakdown:
Clinical Interpretation
Example Case
Complex Kidney Stone Case
Stone size: 25mm × 20mm = 500 mm² (1 point)
Tract length: 120 mm (1 point)
Hydronephrosis: Moderate (1 point)
Calyces affected: 3 calyces (1 point)
Stone density: 1200 HU (1 point)
STONE Score Calculation
Total Score: 1 + 1 + 1 + 1 + 1 = 5 points
Success Probability: 93.6%
Risk Category: Low-Moderate Risk
STONE Mnemonic
Stone Size
Length × Width (mm²)
0-3 points
Tract Length
Skin to stone distance
0-1 points
Obstruction
Hydronephrosis severity
0-1 points
Number
Calyces with calculi
0-2 points
Essence
Stone density (HU)
0-1 points
PCNL Tips
CT scan required for accurate measurements
Lower scores indicate higher success rates
Consider patient comorbidities
Alternative treatments for high-risk cases
Understanding the STONE Scoring System
What is PCNL?
Percutaneous nephrolithotomy (PCNL) is a minimally invasive surgical procedure to remove large kidney stones (>1.5 cm) or complex stones that cannot be treated with other methods. The procedure involves creating a small incision in the back to access the kidney directly.
Why Use STONE Score?
- •Predicts stone-free outcome after first PCNL
- •Helps with treatment planning and patient counseling
- •Identifies cases requiring alternative approaches
- •Evidence-based risk stratification
PCNL Procedure Steps
1. Access Creation
Percutaneous tract from skin to kidney
2. Stone Fragmentation
Ultrasonic or laser lithotripsy
3. Fragment Removal
Suction and extraction of stone pieces
4. Nephrostomy
Temporary tube placement for drainage
⚠️ Medical Disclaimer
This calculator is for educational purposes only and should not replace professional medical advice. The STONE score is a predictive tool that helps estimate success probability but does not guarantee outcomes. Always consult with a qualified urologist for treatment decisions. Patient factors, surgeon experience, and institutional factors may influence actual outcomes.