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Year : 2011  |  Volume : 27  |  Issue : 4  |  Page : 568-569

How accurate is the "Guy's stone score" for predicting the stone-free rates after percutaneous nephrolithotomy?


Date of Web Publication4-Jan-2012

Correspondence Address:
Swarnendu Mandal

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Source of Support: None, Conflict of Interest: None

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How to cite this article:
Mandal S. How accurate is the "Guy's stone score" for predicting the stone-free rates after percutaneous nephrolithotomy?. Indian J Urol 2011;27:568-9

How to cite this URL:
Mandal S. How accurate is the "Guy's stone score" for predicting the stone-free rates after percutaneous nephrolithotomy?. Indian J Urol [serial online] 2011 [cited 2022 Jul 6];27:568-9. Available from:

Thomas K, Smith NC, Hegarty N and Glasse JM. The Guy′s Stone Score-Grading the Complexity of Percutaneous Nephrolithotomy Procedures. Urology.2011;77:277-81

   Summary Top

Currently, there is no standardized method available to predict the stone-free rate (SFR) after percutaneous nephrolithotomy (PCNL). The authors in this study report the development and validation of "Guy's stone score", a scoring system to predict the SFR after PCNL. The stone-free status was defined as no visible stones or the presence of clinically insignificant residual fragments <4 mm on plain abdominal radiography or ultrasonography or computed tomography (CT) for radiolucent calculi, done 6 weeks after PCNL.

The study was conducted in three parts: First was to develop the stone score; second was to assess the reproducibility; and third was to validate it. For the development stage, an initial score was agreed using evidence from the published data, combined with the knowledge and experience of endourologists. [1] The score was independently applied to 20 consecutive PCNL cases. The process was then repeated on an additional 10 cases after refinements.

To assess the reproducibility of the score, an additional 40 consecutive PCNL cases were independently scored by clinicians who were unaware of the patient's outcomes. The patients were scored according to the preoperative and or intraoperative imaging findings. Inter-rater agreement was calculated using the "free marginal kappa coefficient" which is a chance-adjusted measure of agreement, using the online kappa calculator.

To validate the score, it was applied to 100 consecutive PCNL procedures. Multivariate linear regression analysis was used to investigate the factors potentially affecting the SFR, complication rate and severity (Clavien grade), operation time, and radiation time and exposure. These factors were the stone score, stone burden (surface area), operating surgeon, patient's weight, age, comorbidity, and urine culture findings.

The score comprised four grades: Grade I, solitary stone in mid/lower pole or solitary stone in the pelvis with simple anatomy; grade II, solitary stone in upper pole or multiple stones in a patient with simple anatomy or a solitary stone in a patient with abnormal anatomy; grade III, multiple stones in a patient with abnormal anatomy or stones in a caliceal diverticulum or partial staghorn calculus; grade IV, staghorn calculus or any stone in a patient with spina bifida or spinal injury. The SFR for grade I, II, III and IV were 81%, 72%, 35% and 29%, respectively. Multivariate linear regression analysis (SPSS) revealed that the Guy's stone score was the only factor that significantly and independently predicted the SFR (P=0.01). None of the other factors (i.e., stone burden, operating surgeon, patient's weight, age, comorbidity, and urine culture) correlated statistically significantly with the SFR.

   Comments Top

With the success of PCNL to treat large renal calculi, open surgery is now rarely necessary. [2] Although minimally invasive, PCNL is a major operation and does not always render the patient stone-free. Clear benefits exist in having a standardized method of predicting the SFR after PCNL. Patients could be more accurately counseled preoperatively about the chance of becoming stone-free after their procedure. It would facilitate the objective assessment of technical modifications. Surgeons can use it to compare their own SFR against the predicted SFR and publications in this field can be more objectively analyzed. It could also aid in referral of complex cases into specialist centers. A number of approaches to classifying PCNL have been attempted, but none of these are in common use. Tefekli et al.[3] divided stones into simple (isolated renal pelvis or isolated caliceal stones) and complex (partial or staghorn, renal pelvis stones accompanying caliceal stones, regardless of size). They did not find a consistent correlation between the severities of the complications and complexity but did find a non-statistically significant greater success rate for "simple" stones compared with "complex" ones. The ideal method of predicting the outcomes after PCNL would be a scoring system that is quick, simple and reproducible and has a good correlation with the SFR. Progress in the field of technical refinements for PCNL would be easier to monitor with a reliable grading system. [4]

The Guy's stone score accurately predicted the SFR after PCNL. It is easy to use and reproducible. It can be used as an objective and reliable method for describing the complexity of PCNLs when predicting the SFR, stratifying cases between surgeons of different experience, and reporting results. [5]

   References Top

1.Turk C, Knoll T, Petrik A, Sarica K, Straub M, Seitz C. Guidelines on urolithiasis. Eur Assoc Urol. 2010:1106.  Back to cited text no. 1
2.Fernstrom I, Johannson B. Percutaneous pyelolithotomy: A new extraction technique. Scand J Urol Nephrol 1976;10:257-9.  Back to cited text no. 2
3.Tefekli A, Ali-Karadag M, Tepeler K, Sari E, Berberoglu Y, Baykal M, et al. Classification of percutaneous nephrolithotomy complications using the modified Clavien grading system: Looking for a standard. Eur Urol 2008;53:184-90.  Back to cited text no. 3
4.De Sio M, Autorino G, Quarto F, Damiano R, Giugliano F, Mordente S, et al. Modified supine versus prone position in percutaneous nephrolithotomy for renal stones treatable with a single percutaneous access: A prospective randomized trial. Eur Urol 2008;54:196-203.  Back to cited text no. 4
5.Thomas K, Smith NC, Hegarty N and Glasse JM. The Guy's Stone Score-Grading the Complexity of Percutaneous Nephrolithotomy Procedures. Urology.2011;77:277-81.  Back to cited text no. 5


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