Kidney STONE Score

Prognoses renal calculi free outcome after first intervention.

Read more about the x-ray findings used in the calculator and about the original study in the text below the form.

The STONE score calculator analyses the clinical radiologic evidence after the first percutaneous nephrolithotomy to check the patient’s likelihood to be free of kidney stones.

The STONE result is directly correlated with the probability of kidney stone free outcome after percutaneous nephrolithotomy:

STONE result Probability of stone free outcome after first procedure
5 94%
6 92%
7 88%
8 83%
9 64%
10 42%
≥11 27%


Stone size (mm2)


Tract length (mm)


Obstruction (Hydronephrosis)


Number of calyces with calculi


Stone density in HU

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Steps on how to print your input & results:

1. Fill in the calculator/tool with your values and/or your answer choices and press Calculate.

2. Then you can click on the Print button to open a PDF in a separate window with the inputs and results. You can further save the PDF or print it.

Please note that once you have closed the PDF you need to click on the Calculate button before you try opening it again, otherwise the input and/or results may not appear in the pdf.


Parameters considered

The above calculator is a prognosis method used to check the stone free outcome chances of patients who undergo percutaneous nephrolithotomy.

There are five reproducible parameters available from preoperative noncontrast-enhanced computed tomography analysed in the method, known under the STONE mnemonic:

Stone size (mm2) – size is defined as lesion length multiplied by width;

Tract length (mm) – indicates the distance from stone center to skin, measured on CT film at 0°, 45°, and 90°;

Obstruction – also known as hydronephrosis;

Number of calyces with calculi – defines the number of aggregations in the minor or major calyx;

Essence – defines the stone density in Hounsflied units.

A 2014 study published in the Journal of the American Society of Nephrology emphases the need for newer and more sensitive methods of kidney stone prevention and risk stratification, as recurrence rates soar.

There are several risk factors for recurrent renal calculi:

■ Family or personal history of kidney stones;

■ Personal history of UTIs;

■ Personal history of small intestine disease, inflammation or surgery;

■ Treatment with aspirin, diuretics, anti-acids or calcium supplements;

■ Sedentary life style;

■ A high protein diet.


Result interpretation

The result from the STONE calculator is correlated with kidney stone recurrence after first successful percutaneous nephrolithotomy intervention.

STONE result Probability of stone free outcome after first procedure
5 94%
6 92%
7 88%
8 83%
9 64%
10 42%
≥11 27%

About the study

The prognosis method for stone free rates was created by Okhunov et al. in 2013, following a study on 117 patients.

The mean score following assessment with the STONE method was 7.7 whilst all results were in the range 4 to 11.

The stone free rate after the first procedure was found to be 80%. It was also found that patients deemed stone free after intervention had significantly lower scores than patients with residual stones.

Since it is based on standardized parameters, the method was found to be accurate in predicting treatment outcome and the risk of perioperative complications.


Percutaneous nephrolithotomy explained

PCNL is the medical procedure in which keyhole surgery is performed on kidney stones larger than 1.5 cm and localized in the lower pole of the kidney or in the ureter.

The intervention is performed under general anesthesia and is considered a simple one in patient with no risk factors or comorbidities.

During ultrasound or x-ray monitoring of the kidney area, a fine bore tube is passed with the help of a cystoscope through the bladder.

A wire is passed in that location into the kidney. What follows is the placement of a rigid tube through a 1 cm cut. In some cases, where the stone dimension is bigger, several incisions and fragmenting may be necessary. A nephroscope is used to visualize the stone and facilitate the extraction.

After intervention, recovery lasts between 4 to 6 hospital days. X-ray tests are used to check whether there are any more residual stone fragments, which is a common complication of the procedure.

Post procedure complications include massive hemorrhage in need for blood transfusion, damage to the spleen or liver or embolization of renal arteries.


Original source

Okhunov Z, Friedlander JI, George AK, Duty BD, Moreira DM, Srinivasan AK, Hillelsohn J, Smith AD, Okeke Z. S.T.O.N.E. nephrolithometry: novel surgical classification system for kidney calculi. Urology. 2013; 81(6):1154-9.


Akhavein A, Henriksen C, Syed J, Bird VG. Prediction of single procedure success rate using S.T.O.N.E. nephrolithometry surgical classification system with strict criteria for surgical outcome. Urology. 2015; 85(1):69-73.

Other references

1. Kuzgunbay B, Gul U, Turunc T, Egilmez T, Ozkardes H, Yaycioglu O. Long-term renal function and stone recurrence after percutaneous nephrolithotomy in patients with renal insufficiency. J Endourol. 2010; 24(2):305-8.

2. Labadie K et al. Evaluation and Comparison of Urolithiasis Scoring Systems in Percutaneous Kidney Stone Surgery. Journal of Urology. 2015; 193 (1): 154-9.

3. Eisner BH, Goldfarb DS. A Nomogram for the Prediction of Kidney Stone Recurrence. J Am Soc Nephrol. 2014; 25(12): 2685–2687.

Specialty: Nephrology

System: Urinary

Objective: Prognosis

Type: Calculator

No. Of Items: 5

Year Of Study: 2013

Abbreviation: STONE

Article By: Denise Nedea

Published On: May 30, 2017

Last Checked: May 30, 2017

Next Review: May 30, 2023