STONE Nephrolithometry Score
Predict PCNL outcomes using the validated STONE score. Five CT-based componentsโSize, Tract, Obstruction, Number, Essenceโstratify stone-free rates and complication risks.
Why This Health Metric Matters
Why: Accurate outcome prediction helps urologists counsel patients and plan surgical approaches.
How: Sum five component scores (5โ16). Lower scores predict higher stone-free rates and fewer complications.
- โScores โค5: ~93% SFR
- โScores 9โ11: ~64% SFR
- โStaghorn: ~45% SFR
๐ฅ Sample Clinical Scenarios โ Click to Load
Stone and Anatomy Assessment
Enter stone characteristics from preoperative CT imaging
โ ๏ธFor informational purposes only โ not medical advice. Consult a healthcare professional before acting on results.
๐ฅ Health Facts
5โ16 point range
โ Journal of Urology
76โ98% SFR for >2cm stones
โ AUA/EAU
๐ Key Takeaways
- โข The STONE score is a validated nephrolithometry scoring system that predicts outcomes after percutaneous nephrolithotomy (PCNL)
- โข Scores range from 5 to 16 โ lower scores predict higher stone-free rates and fewer complications
- โข Five factors are assessed: Size, Tract length, Obstruction, Number of stones, and Essence (density)
- โข Patients with scores โค5 have stone-free rates above 90%, while scores โฅ9 drop below 65%
- โข This tool helps urologists counsel patients on expected outcomes and plan surgical approaches
๐ก Did You Know?
๐ How the STONE Scoring System Works
The STONE score uses five objective CT-based measurements to generate a composite score (5-16 points) that correlates with PCNL outcomes.
Step 1: Obtain Non-Contrast CT
High-quality non-contrast CT is essential for accurate measurements of stone size, density, and tract planning.
Step 2: Measure Each Component
S (Stone size): length ร width ร 0.25 ร ฯ. T (Tract): skin-to-stone distance. O (Obstruction): hydronephrosis grade. N (Number): calyces involved. E (Essence): Hounsfield units.
Step 3: Sum and Stratify
Total score 5-6 = Low complexity (~93% SFR). 7-8 = Moderate (~83%). 9-11 = High (~64%). 12+ = Very high (~45%).
๐ฏ Expert Tips for PCNL Planning
๐ก Preoperative Optimization
Ensure sterile urine before PCNL. Treat UTI, stop anticoagulation per protocol, and review CT for calyceal anatomy.
๐ก Posterior Calyx Access
Posterior calyx access is preferred to avoid major vessels. Upper pole access may require supracostal approach.
๐ก Stone Density Matters
Stones >1100 HU fragment poorly. Consider laser settings and expect longer operative time for dense stones.
๐ก Staged Procedures
For STONE score โฅ9, plan for possible second-look procedure. Nephrostomy tube facilitates re-entry.
โ๏ธ STONE vs Other Scoring Systems
| Feature | STONE Score | Guy's Score | S.T.O.N.E. |
|---|---|---|---|
| Variables | 5 (S,T,O,N,E) | 4 | 5 |
| CT-based | โ | โ | โ |
| Stone-free prediction | โ | โ | โ |
| Complication prediction | โ | โ ๏ธ Limited | โ |
| Validation | Multi-center | Single center | Multi-center |
| Range | 5-16 | 1-4 | 5-13 |
โ Frequently Asked Questions
What is the STONE nephrolithometry score?
It is a CT-based scoring system that uses five variables (Stone size, Tract length, Obstruction, Number of stones, Essence/density) to predict percutaneous nephrolithotomy outcomes including stone-free rates and complication risks.
When should PCNL be considered over ESWL or ureteroscopy?
PCNL is generally recommended for stones >2cm, staghorn calculi, lower pole stones >1cm, and stones resistant to ESWL (density >1000 HU). The STONE score helps quantify expected outcomes.
How accurate is the STONE score?
Validation studies show the STONE score has good predictive accuracy (AUC 0.70-0.75) for stone-free status after PCNL. It performs best for stratifying risk categories rather than precise percentage predictions.
What is considered a good STONE score for surgery?
Scores โค5 indicate favorable anatomy with >90% stone-free rates. Scores 6-8 are intermediate. Scores โฅ9 suggest complex cases that may require multiple procedures or access tracts.
What is PCNL?
Percutaneous nephrolithotomy (PCNL) is a minimally invasive surgical procedure to remove kidney stones through a small incision in the back. A nephroscope is passed through a tract into the kidney to fragment and extract stones.
How is stone surface area calculated?
Stone surface area is calculated from CT measurements using the formula: Length ร Width ร ฯ ร 0.25. For irregular or branched stones, the areas of each component should be summed.
Why is stone density important?
Stone density (Hounsfield units) predicts stone hardness and fragmentation difficulty. Low-density stones (<950 HU) are often uric acid and fragment easily. High-density stones (>1100 HU) like calcium oxalate monohydrate are harder.
What complications can occur with PCNL?
Potential complications include bleeding (may require transfusion in 5-10%), infection/sepsis, injury to adjacent organs, urine leak, residual fragments requiring additional procedures. Higher STONE scores correlate with higher complication rates.
๐ Kidney Stone & PCNL by the Numbers
๐ Official Data Sources
โ ๏ธ Disclaimer: This calculator is for educational and research purposes only. Clinical decisions should always be made in consultation with the treating urology team. Patient-specific factors not captured by the STONE score may significantly affect outcomes. The STONE score provides estimates based on published data and may not reflect outcomes at all institutions.