Discussion: in spite of obese patients (BMI >35) having larger stone burden and greater ASA score, BMI did not significantly impact on PCNL outcomes. Such findings may be useful in counseling patients regarding this procedure. SC327 A nomogram to predict significant estimated glomerular filtration rate reduction after percutaneous nephrolithotomy U. Falagario, A. Martini, A. Mangiatordi, M. Auciello, V. Mancini, G. Carrieri, L. Cormio (Foggia) Aim of the study: Percutaneous nephrolithotomy (PCNL) is a minimally invasive technique to treat large or otherwise complex renal or proximal ureteral stones. Though considered a safe procedure, it may cause acute kidney injury (AKI) due to puncturing and dilating the renal parenchyma as well as to release of bacteria from the stone. Moreover, stone themselves may cause obstructive uropathy. Indeed, the reported rate of AKI after PCNL ranges from 6.7% to 38.2% in different series and may to poor postoperative outcomes and a longer hospital or intensive care unit stay. In the present study we attempted to develop a nomogram to predict AKI following PCNL. Materials and methods: Our prospectively maintained Internal Review Board approved PCNL database was queried. Final study population included 605 patients with complete clinical data. Patient characteristics, preoperative laboratory values, intraoperative data, and stone characteristics were collected. Estimated GFR (eGFR) was calculated according to the Chronic Kidney Disease Epidemiology Collaboration formula. Patients with eGFR < 30 were excluded from the analysis. AKI was defined as >25% reduction in preoperative baseline eGFR or >1.5-fold increase in preoperative creatinine, both at discharge from hospital. A nomogram was built based on a binary logistic regression that ultimately included age, sex, baseline eGFR and Operative time. Internal validation was performed using the leave- one-out cross validation. Calibration was graphically investigated. The decision curve analysis was used to evaluate the net clinical benefit. Results: Descriptive characteristics are shown in Table 1. Median (IQR) age at surgery was 54.8 (43.8, 63.4) years; 320 (52.9%) patients were female, while 285 (47.1%) were male. Median (IQR) eGFR was 86.3 (71.9, 99.7) ml/min/1.73 m2. Median (IQR) Operative time was 75.0 (60.0,100.0) min. Postoperative AKI occurred in 65 (10.7%) patients. All variables fitted in the model significantly (p < 0.01) predicted AKI and were therefore used to build a nomogram (Figure 1). After internal validation, the AUC was 82%. The model demonstrated excellent calibration and improved clinical risk prediction at the decision curve analysis. Discussion: We developed a nomogram that accurately predicts AKI in patients undergoing PCNL. This model may serve in the preoperative setting to counsel patients regarding their risk of suffering AKI as well as in the immediate postoperative. SC328 Is it possible to characterize urinary stone composition and stiffness using dual-energy CT (DECT)? an in vitro study: DECT compared to infrared spectroscopy (SC-IR) C. Capretti, A. Cameli, F. Sbaraglia, L. Pierini, A. Mari, M. Misericordia, G. Milanese, A. Giovagnoni, A. Galosi (Ancona) Aim of the study: The aim of this study was to evaluate the diagnostic accuracy of last generation dual-energy CT (DECT) in characterize chemical composition of urinary stones, previously underwent single- energy CT (SECT) scans and analyzed with infrared spectroscopy (SC- IR), which is currently considered the best diagnostic method for the chemical stones analysis. Materials and methods: 65 urinary stones, spontaneously expelled or surgically treated, were collected in a period between December 2017 and December 2018.The stones composition was triple-blind studied with SC-IR, DECT and SECT. SC-IR was associated with the empirical operator-dependent evaluation of the stones stiffness. 17 phantoms have been prepared, each one containing stones of the same SC-IR composition and stiffness, ordered by maximum to minimum diameter (from 1.2 cm to 0.2 cm) and put in a test tube filled with a gel having urine CT density (9 HU). The DECT protocol included three scans for each kVp range: 70–150; 80–140; 80–150; 90–150; 100–150. DECT scans were subsequently processed at Syngo.via workstation with the automatic dual energy analysis pathway “kidney stone”. Results: 12 pure stones < 4 mm were not detected. 22 of 23 Uric Acid (UA) stones were recognized with an accuracy of 96%.10 of 10 oxalate stones were recognized as such with an accuracy of 100%. The phantom containing 20 mixed stones was excluded from the results. Comparison between mixed DECT scans and standard 120kV SECT scan showed a mean difference of +50 HU for SECT scans than DECT for UA stones, for Oxalates the difference was in a range between +150 HU for di-Hydrate stones and +400 Hu for mono-Hydrate stones (Tab.1). Moreover, our analysis, combining HU values from DECTacquisitions, permitted a differentiation of the stones stiffness. The HU sum normalized for strong UA stones was 0.716 ± 0.071 (median ± ds), for intermediate stiffness UA stones the value was 0.592 ± 0.082 and for the soft UA stones was 0.535±0.014 (Fig A; Tab.2). For the oxalates stones it was possible not only to differentiate the stiffness, but also the nature of components (mono or di-Hydrate): 1.496 ± 0.245 for the mono-Hydrate oxalate stones with strong stiffness; 0.946 ± 0.056 for European Urology Supplements 18(9) (2019), e3155–e3376 e3350