BACKGROUND AND OBJECTIVE: Stone size has traditionally been measured in one dimension. This is reflected in most of the literature and in the EAU guidelines. However, recent studies have shown that multidimensional measures provide better prediction of outcomes. METHODS: We performed a systematic review and meta-analysis of the prognostic accuracy of measures of stone size (PROSPERO reference CRD42022346967). We considered all studies reporting prognostic accuracy statistics on any intervention for kidney stones (extracorporeal shockwave lithotripsy [ESWL], ureterorenoscopy [URS], or percutaneous nephrolithotomy [PCNL]; Population) using multiplane measurements of stone burden (area in mm2 or volume in mm3; Intervention) in comparison to single-plane measurements of stone burden (size in mm; Intervention) for the study-defined stone-free rate (Outcome) in a PICO-framed question. We also assessed complication rates (overall and by Clavien-Dindo grade) and the operative time as secondary outcomes. Searches were made between 1970 and August 2023. We used the DeLong method to compare receiver operating characteristic (ROC) curves. KEY FINDINGS AND LIMITATIONS: Of 24 studies included in the review, 12 were eligible for comparative analysis with the DeLong test following meta-analysis of prognostic accuracy. For prediction of stone-free status, the area under the ROC curve (AUC) was significantly higher for stone volume than for stone size (0.71 vs 0.67; p < 0.001). Subanalyses confirmed this for ESWL and URS, but not for PCNL. For URS, the AUC was also significantly higher for stone area than for stone size (0.79 vs 0.77; p < 0.001). Throughout all analyses, there was no difference in AUC between stone area and stone volume. There was high risk of bias for all analyses apart from the URS subanalyses. CONCLUSIONS AND CLINICAL IMPLICATIONS: According to the limited data currently available, stone-free rates are predicted with significantly higher accuracy using multidimensional measures of stone burden in comparison to a single linear measurement. PATIENT SUMMARY: We reviewed different ways of measuring the size of stones in the kidney or urinary tract and compared their accuracy in predicting stone-free rates after treatment. We found that measurement of the stone area (2 dimensions) or stone volume (3 dimensions) is better than stone diameter (1 dimension) in predicting stone-free status after treatment.

Department of Surgery Royal College of Surgeons in Ireland Dublin Ireland

Department of Urology 1st Faculty of Medicine Charles University Prague Czechia

Department of Urology and Renal Transplantation Aix Marseille University Marseille France

Department of Urology Beaumont Hospital Dublin Ireland

Department of Urology Bruederkrankenhaus Trier Johannes Gutenberg University Mainz Trier Germany

Department of Urology Freeman Hospital Newcastle upon Tyne UK

Department of Urology National and Kapodistrian University of Athens Sismanogleio Hospital Athens Greece

Department of Urology University Hospital of Ghent Ghent Belgium

Department of Urology University Hospital Southampton NHS Foundation Trust Southampton UK

Department of Urology University of Southern Denmark Odense Denmark

Division of Nephrology and Dialysis Department of Medicine University of Verona Verona Italy

Sant'Andrea Hospital Sapienza University Rome Italy

Urolithiasis Guidelines Panel European Association of Urology Arnhem The Netherlands

Young Academic Urologists Urolithiasis Working Group European Association of Urology Arnhem The Netherlands

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