Evaluation of various nephrometric scoring system for nephrolithiasis to predict stone free status after percutaneous nephrolithotomy: A comparative study

Abstract

Background:

The CROES Nephrolithometry nomogram, S.T.O.N.E. Nephrolithometry Score and Guy’s stone score were introduced for stratification of kidney stones disease on the basis of quantitative stone burden and its distribution. Till date there has been very limited data on head to head comparison of the existing scoring systems. Comparison and analyses among the scoring system helps in further refinement of these systems along with development of new more effective and broadly acceptable nomogram.

Objective:

Predictability of the stone-free status (SFS) and post-operative complication after PCNL by various scoring systems (The CROES nomogram, S.T.O.N.E. nephrolithometry score and Guy’s stone score).

Materials and Methods:

Total 100 adult patients underwent PCNL after considering inclusion and exclusion criteria. All patients underwent Preoperative NCCT scan, investigations of blood (Hb%, PCV, bleeding and coagulation profile, urea, and creatinine), and urine (RE/ME and C/S), Postoperative X ray KUB/NCCT.

Results:

ROC curves were developed for each scoring system to determine the accuracy to predict stone free status. We found CS had significantly higher AUC than other scoring systems [p-value for CS vs GSS = 0.0091 & CS vs SS = 0.000]. So CS has higher accuracy to predict stone free status. None of the scoring system had shown significantly higher AUC than other scoring system in predicting complication.

Conclusion:

CROES Nephrolithometry nomogram is most accurate to predict preoperative stone-free rate. All scoring systems can equally predict perioperative complications and other variables.

Keywords

PCNL stone-free status guy’s stone score CROES nomogram STONE nephrolithometry score

Introduction

Percutaneous nephrolithotomy (PCNL) is procedure of choice for renal stone treatment with very low incidence of serious adverse events.^1,2 Kidney stone complexity assessment by computed tomography (CT) Scan has become common practice. CT scan image provides accurate stone size estimation along with its distribution in pelvicalyceal system, and pelvicalyceal anomalies if any.

The S.T.O.N.E. Nephrolithometry Score,³ and the CROES Nephrolithometry nomogram,⁴ The Guy’s stone score⁵ were introduced for stratification of kidney stone disease on the basis of stone burden, location and its complexity. These scoring nomogram helps in disease categorization tools that ultimately improves patient counselling regarding post-operative outcome and stone clearance and also helps in surgical planning.^3,5

Till date there has been very limited data on head to head comparison among existing scoring nomograms. Comparison and analyses of among the scoring system helps in further refinement of these system along with development of new more effective and broadly acceptable nomogram. Thus, we have compared these scoring nomogram for post-operative outcome of PCNL.

Aims and objectives

Primary outcome was ability to predict the stone clearance after PCNL among the scoring systems (CROES nomogram, S.T.O.N.E. nephrolithometry score and the Guy’s stone score). Secondary outcomes were the ability to predict peri and intra operative variables like fluoroscopy time (FT), scope time (ST) procedure time (PT) and length of hospital stay (LOS) and post-operative using modified Clavien-Dindo system.

Materials and methods

Our study design was hospital based prospective observational study conducted in the department of Urology in a tertiary care hospital of eastern India. Total 100 patients, who underwent PCNL during study period were assessed after meeting study eligibility criteria and taking informed written consent. Inclusion criteria were all adult patient > 18 years, patients undergoing PCNL and exclusion criteria were patients without pre-operative NCCT scan of the abdomen, age < 18 years, pre-operative ureteral stent or nephrostomy tube placement in ipsilateral kidney, staged PCNL procedures and patients who had underwent any additional procedure in the same setting. All patients underwent preoperative NCCT scan, investigations of blood (Hb%, PCV, bleeding and coagulation profile, urea, creatinine) and urine (RE/ME and C/S), postoperative X ray KUB/NCCT. Demographic profile of the patients [comorbidities, BMI (Body Mass Index), and preoperative blood levels] were recorded. Stone characteristics were documented for each stone. CROES score, STONE score and Guy’s stone score were calculated for all patients. All PCNL procedures were done in standard prone position technique. Perioperative data [Procedure time (PT), Scope Time (ST), Fluoroscopy Time (FT), hospital stay and post-operative complications if any (modified Clavien-Dindo grading system)] were recorded. Stone free rate according to postoperative x-ray KUB/NCCT (for radiolucent stones).

Statistical analysis

Data was compiled in Excel spread sheet to prepare the master chart and then analyzed with MedCalc17.9.6. IBM SPSS Statistics 23.0. Categorical data were analyzed using “Pearson Chi-Square” test and continuous data were analyzed using Unpaired t-test. “General Linear Model” was applied for “Tests of Within Subject Effects” with a good fit to the present data (Mauchly’s Test of Sphericity). Mann-Whitney U-test done for ordinal data. Area under curve (AUC) for each scoring systems for ability to predict stone clearance status and post-operative complications were calculated from receiver operating characteristics (ROC) curves and compared. All tests of significance were calculated at 5% absolute precision with p-value of < 0.05.

Result

In our study, we had included total 100 patients after matching inclusion and exclusion criteria. The demographic profile our patients and stone characteristics of them are furnished according to the clearance status in Table 1.

Table 1.

Profile of patients and characteristics of stones.

Variables	Stone clearance group (SCG)	Incomplete stone clearance group (ISCG)	p Value
No. of patients	71	29
Sex
Male	42	16	0.714
Female	29	13	0.714
Age (years) [Mean ± SD]	38.77 ± 11.11	39.34 ± 12.85	0.824
Charlson comorbidity index
0	55	22	0.996
1	12	5
2	2	1
3	2	1
BMI [Mean ± SD] (Body mass index)	23.42 ± 3.45	24.11 ± 3.23	0.359
Preoperative Hb (gm/dl) [Mean ± SD]	13.60 ± 1.61	14.00 ± 1.99	0.296
Preoperative PCV [Mean ± SD] (Packed call volume)	40.11 ± 4.58	41.62 ± 5.69	0.168
Laterality of stone
Right	39	21	0.105
Left	32	8	0.105
Stone burden (mm²) [Mean ± SD]	415.87 ± 292.08	740.82 ± 259.79	<0.0001
Hounsfield units of stones [Mean ± SD]	1096.65 ± 161.35	1006.00 ± 127.85	0.008
Implicated calyces
Single	48	1	<0.0001
Multiple	23	28	<0.0001
Presence of staghorn calculus
Staghorn calculus	1	5	0.0025
Non-staghorn calculus	70	24	0.0025
Number of access
1	69	25	0.036
2	2	4	0.036
Access type
Infracostal	64	20	0.025
Supracostal	5	5
Combined	2	4
CROES Score [Mean ± SD]	233.33 ± 56.66	140.88 ± 28.02	<0.0001
Stone Score [Mean rank and Sum of Ranks]	42.54 and 3020.50	69.98 and 2029.50	<0.0001
Guy’s Stone Score [Mean rank and Sum of Ranks]	40.44 and 2871.50	75.12 and 2178.50	<0.0001

Overall stone clearance rate after PCNL in our study was 71%. Most of our patients were male (58%). We divided our patients into two groups according to stone clearance status. Both the groups were statistically equivalent in terms of sex distribution, age, BMI, comorbidities, preoperative hemoglobin levels and laterality of stones. Presence of staghorn calculus, involvement of multiple calyces and higher stone burden were significantly higher in residual stone group; whereas CROES score, Hounsfield units of stones, single access and infra-costal access during operation were significantly higher in stone free group. Stone clearance rate of each scoring nomogram were calculated and shown in Table 2.

Table 2.

Stone free status of various scoring nomogram.

Scoring system	No. stone free/Total no.	Percentage
CS
⩽129	1/10	10
130–169	11/28	39.29
170–219	16/18	88.89
⩾220	43/44	97.73
SS
5–6	37/42	88.09
7–8	32/44	72.73
9–13	2/14	14.29
GSS
I	38/39	97.44
II	28/40	70
III	4/15	26.67
IV	1/6	16.67

CS: the CROES (Clinical Research Office of Endourological Society) score; SS: S.T.O.N.E. Nephrolithometry Score; GSS: Guy’s Stone Score.

ROC curves was generated to determine the accuracy to predict stone free status (Figure 1(a)) for each scoring system. We found CS had significantly higher AUC than other scoring systems. So CS has higher accuracy to predict stone free status. Now ROC curves were developed for each scoring systems to determine the accuracy to predict complications (Figure 1(b)). None of the scoring system had shown significantly higher AUC than other scoring system in predicting complication.

Figure 1.

(a) ROC for scoring systems for predicting SFS and (b) ROC for scoring systems for predicting complications.

Our patients were then evaluated for procedure time (PT), scope time (ST), fluoroscopy time (FT), hospital stay and post-operative complication rate (modified Clavien-Dindo Classification) among the different scoring system group. Results are shown in Table 3.

Table 3.

Peri-operative variable And length of hospital stay among different scoring system group.

Perioperative variables	CS groups		SS groups		GSS groups
Perioperative variables	Groups	p Value	Groups	p Value	Groups	p Value
PT (minutes) [Mean ± SD]	CS 1 [98.70 ± 22.56	<0.0001	SS 1 [78.33 ± 17.13]	<0.0001	GSS I [75.15 ± 17.60]	<0.0001
	CS 2 [94.21 ± 19.04]		SS 2 [84.02 ± 19.43]		GSS II [86.53 ± 17.37]
	CS 3 [85.17 ± 13.50]		SS 3 [103.36 ± 19.29]		GSS III [89.00 ± 18.73]
	CS 4 [74.45 ± 17.46]				GSS IV [117.83 ± 11.75]
ST (minutes) [Mean ± SD]	CS 1 [64.00 ± 19.97]	<0.0001	SS 1 [47.12 ± 16.43]	0.001	GSS I [43.23 ± 15.17]	<0.0001
	CS 2 [62.25 ± 17.04]		SS 2 [53.02 ± 17.24]		GSS II [56.08 ± 16.42]
	CS 3 [54.33 ± 12.78]		SS 3 [66.79 ± 16.94]		GSS III [56.53 ± 16.63]
	CS 4 [42.86 ± 14.74]				GSS IV [78.33 ± 9.31]
FT (minutes) [Mean ± SD]	CS 1 [8.60 ± 2.50]	<0.0001	SS 1 [6.07 ± 2.52]	0.046	GSS I [5.72 ± 2.28]	0.003
	CS 2 [7.61 ± 2.87]		SS 2 [6.98 ± 2.58]		GSS II [7.18 ± 2.61]
	CS 3 [6.33 ± 1.94]		SS 3 [7.93 ± 2.53]		GSS III [6.27 ± 2.69]
	CS 4 [5.61 ± 2.21]				GSS IV [9.33 ± 1.51]
Hospital stay (days) [Mean ± SD]	CS 1 [5.40 ± 1.35]	0.08	SS 1 [4.60 ± 0.96]	0.065	GSS I [4.59 ± 0.99]	0.363
	CS 2 [4.50 ± 0.84]		SS 2 [4.52 ± 0.88]		GSS II [4.65 ± 1.05]
	CS 3 [4.67 ± 0.97]		SS 3 [5.21 ± 1.25]		GSS III [4.53 ± 0.64]
	CS 4 [4.57 ± 0.95]				GSS IV [5.33 ± 1.21]

PT: procedure time; ST: scopy time; FT: fluoroscopy time.

Discussion

Although there are different developmental concepts for all three scoring systems, these scoring systems are developed for disease stratification tools, predictability of stone free status and postoperative complication along with better patient pre-operative counseling.^4–6 Combining CROES nomogram (CS), S.T.O.N.E. score (SS), Guy’s stone score (GSS), comprises 11 variables, out of that only four are shared by all, those are stone size, location, number, and staghorn status. The non-shared variables (number of stones, renal anatomy, stone density, tract length, past treatment history, renal pelvic obstruction case volume per year, and spinal abnormality or injury) are included separately in scoring system. Abnormal pelvicalyceal anatomy and diverticular stone has been included only in GSS. However, from large scale study there was no association between abnormal renal anatomy and inferior surgical outcomes.^7,8

We analyzed these scoring systems in a single cohort of subjects who underwent PCNL. Although analysis and direct comparison of scoring nomogram is complex due to its heterogenous nature, these can be compared using reliable statistical methods in single cohort.

In contrast to previous study, our study shows CROES score has more predictive capacity of SFS than other two systems. This discrepancy might be due to the fact that each nomogram was developed based on specific cohort of patients tested, which adds an intrinsic bias favoring predictability. Similar to previous studies, stone size remains most consistent factor to predict perioperative complication and stone free status.⁸

In addition to the primary outcome, three scoring systems were significantly associated with intra-operative outcomes (PT, ST, and FT). Previous study showed that it is the urologist’s decision to use the preferred scoring system as all three systems have equal predictive abilities. In our study, CROES nomogram showed its clear superiority over other systems in respect to the secondary outcomes.

In few previous seminal studies external validation of the GSS was reported and this score effectively predicts SFS.^4,9–12 Inter-observer reliability found to be excellent between GSS and S.T.O.N.E. score.^11,13 Kumar et al.¹⁴ concludes that CNN is rather comprehensive scoring system in comparison to GSS with good risk stratification for residual stone after PCNL with disadvantage of cumbersome to use in daily clinical practice.

In our study, none of scoring systems was found inferior than other in predicting post-operative complication. The optimal scoring system should be easy to be implemented, comprehensive and reproducible for standard reporting and comparison in all case.

Labadie et al.¹⁵ concluded that SS is comprehensive with accurate risk stratification and easy applicability than other nomogram because it can be remembered with simple acronym. Since NCCT is investigation of choice for diagnosis and management of urolithiasis, SS seems to be easily implementable with uniform reporting.¹⁰

In contrast recent study by Singla et al.¹⁶ shows all three scoring systems have equal predictability for SFS and post-operative complications. An abbreviation of the S.T.O.N.E. score (S.O.N. score), was proposed by them and it seemed to be equally predictive.

The Table 4 shows results of different Comparative studies of CROES nomogram, S.T.O.N.E. score and Guy’s stone score.

Table 4.

Results of different comparative of CROES nomogram, S.T.O.N.E. score and Guy’s stone score from various study.

Scoring systems	Labadie et al.¹⁵			Tailly et al.¹⁷			Present study
Scoring systems	Grade or score range	Stonefree patients (%)	AUC	Grade or score range	Stonefree patients (%)	AUC	Grade or score range	Stonefree patients (%)	AUC
Guy’s stone score	I	70.2	0.634	I	80.3	0.629	I	97.44	0.847
	II	65.4		II	73.8		II	70
	III	48.1		III	60.5		III	26.67
	IV	35.9		IV	52.3		IV	16.67
S.T.O.N.E. score	5–6	70.6	0.670	5–6	82.1	0.671	5–6	88.09	0.774
	7–8	66.3		7–8	72.7		7–8	72.73
	9–13	46.2		9–13	48.9		9–13	14.29
CROES nomogram	⩽129	22.7	0.671	⩽129	44.4	0.646	⩽129	10	0.936
	130–169	46.4		130–169	64.4		130–169	39.29
	170–219	45.5		170–219	71.8		170–219	88.89
	⩾220	72.7		⩾220	84.2		⩾220	97.73

Possible limitations of study were exclusion of patients with nephrostomy tube or ureteral stent placed pre operatively and prior ipsilateral surgery. Outcome of PCNL in these selected groups of patients is variable and complex. Larger multi-institutional prospective studies are needed to determine a single best scoring system.

Conclusion

Preoperative NCCT scan is an important tool for diagnosis and decision making. CROES Nephrolithometry nomogram is most accurate to predict preoperatively stone-free rate. All scoring systems can equally predict perioperative complications and other variables. The Nephrolithometry scoring systems help to stratify the complexity of PCNL. These help in better patient counselling preoperatively about need for ancillary treatment.

Footnotes

Author contributions

Souvik Chatterjee: Conception, Design, Materials, Data collection and processing, Analysis and Interpretation, Writing. Anand Abhishek: Materials, Analysis and Interpretation, Writing, Literature Review. Kaniska Samanta: Materials, Data collection and processing, Writing. Anupama Ghosh: Analysis and Interpretation, Writing, Critical Review. Soumendra Nath Mandal: Supervision, Writing, Critical Review. Dilip Karmakar: Design, Supervision, Critical Review.

Declaration of conflicting interests

The author(s) declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.

Funding

The author(s) received no financial support for the research, authorship, and/or publication of this article.

Ethics committee approval

Approved by Institutional ethics committee.

• Institute name—Calcutta National Medical, Kolkata, India

• Approval number—CNMC/57/2015

Informed consent

Written informed consent was obtained from the patient for their anonymized information to be published in this article

ORCID iD

Anand Abhishek

References

Scales

Jr Smith

Hanley

, et al. Prevalence of kidney stones in the United States. Urologic Diseases in America Project. Eur Urol 2012; 62: 160–165.

Rudnick

Stoller

ML.

Complications of Percutaneous nephrolithotomy. Can J Urol 1999; 6: 872–875.

Okhunov

Friedlander

George

, et al. S.T.O.N.E. nephrolithometry: novel surgical classification system for kidney calculi. Urology 2013; 81: 1154–1159.

Michel

Trojan

Rassweiler

JJ.

Complications in Percutaneous nephrolithotomy. Eur Urol 2007; 51: 899–906.

Thomas

Smith

Hegarty

, et al. The Guy’s stone score grading the complexity of percutaneous nephrolithotomy procedures. Urology 2011; 78: 277–281.

Smith

Averch

Shahrour

, et al. A Nephrolithometric nomogram to predict treatment success of percutaneous nephrolithotomy. J Urol 2013; 190: 149–156.

Penbegul

Hatipoglu

Bodakci

, et al. Role of ultrasonography in percutaneous renal access in patients with renal anatomic abnormalities. Urology 2013; 81: 938–942.

Osther

Razvi

Liatsikos

, et al. Percutaneous nephrolithotomy among patients with renal anomalies: patient characteristics and outcomes; a subgroup analysis of the clinical research office of the endourological society global percutaneous nephrolithotomy study. J Endourol 2011; 25: 1627–1632.

Mandal

Goel

Kathpalia

, et al. Prospective evaluation of complications using the modified Clavien grading system, and of success rates of percutaneous nephrolithotomy using Guy’s Stone Score: a single-center experience. Indian J Urol 2012; 28: 392–398.

10.

Vicentini

Marchini

Mazzucchi

, et al. Utility of Guy’s stone score based on computed tomographic scan findings for predicting percutaneous nephrolithotomy outcomes. Urology 2014; 83: 1248–1253.

11.

Ingimarsson

Dagrosa

Hyams

, et al. External validation of a preoperative renal stone grading system: reproducibility and inter – rater concordance of the Guy’s Stone Score using preoperative computed tomography and rigorous postoperative stone – free criteria. Urology 2014; 83: 45–49.

12.

Akhavein

Henriksen

Bird

. Prediction of single procedure success rate using S.T.O.N.E. nephrolithometry surgical classification system with strict criteria for surgical outcomes. J Urol 2013; 189(Suppl. 4): e627–e628.

13.

Okhunov

Helmy

Perez-Lansac

, et al. Interobserver reliability and reproducibility of S.T.O.N.E. nephrolithometry for renal calculi. J Endourol 2013; 27: 1303–1306.

14.

Kumar

Sreenivas

Karthikeyan

, et al. Evaluation of CROES nephrolithometry nomogram as a preoperative predictive system for percutaneous nephrolithotomy outcomes. J Endourol 2016; 30(10): 1079–1083.

15.

Labadie

Okhunov

Akhanavein

, et al. Evaluation and comparison of urolithiasis scoring systems used in percutaneous kidney stone surgery. J Urol 2015; 193: 154–159.

16.

Singla

Khattar

Nayyar

, et al. How practical is the application of percutaneous nephrolithotomy scoring systems? Prospective study comparing Guy’s Stone Score, S.T.O.N.E. score and the Clinical Research Office of the Endourological Society (CROES) nomogram. Arab J Urol 2017; 15: 7–16.

17.

Tailly

Okhunov

Nadeau

, et al. Multicenter external validation and comparison of stone scoring systems in predicting outcomes after percutaneous nephrolithotomy. Journal of Endourology 2016; 30(5): 594–601.