Association Between Renal Pelvis Urine Density and the Risk of Infectious Complications after Retrograde Intrarenal Surgery

<b><i>Introduction:</i></b> Renal pelvis urine density (RPUD), as measured by computed tomography (CT), may serve as an effective predictor for pyonephrosis. Our objective was to evaluate the correlation between the likelihood of developing infectious complications post-retrograde intrarenal surgery (RIRS) and RPUD measurements obtained from preoperative CT scans. <b><i>Materials and Methods:</i></b> We retrospectively reviewed data from patients who underwent RIRS for kidney stone treatment at a tertiary care facility between June 2017 and June 2024, using the hospital's database. The patients were divided into two groups based on the development of postoperative infective complications. The groups were compared in terms of preoperative (demographic data, stone characteristic, and RPUD) and operation data. RPUD was measured by creating an ellipse much as possible area encompassing the renal pelvis on the treated side area encompassing the renal pelvis on the treated side, and the average Hounsfield unit (HU) value was recorded. <b><i>Results:</i></b> Postoperative infection developed in 31 of 588 patients (5.3%). The median RPUD value was 15 in the infective group and 8 in the noninfective group, with a statistically significant difference between the groups (<i>p</i> = 0.001). Body mass index, stone burden, stone density, and RPUD were associated with postoperative infection in the multivariate analysis (<i>p</i> = 0.001, <i>p</i> = 0.008, <i>p</i> = 0.007, and <i>p</i> = 0.001, respectively). Each unit increase in RPUD increased the risk of postoperative infection 1.107-fold. The receiver operating characteristic (ROC) analysis demonstrated a significant relationship between RPUD value and the risk of postoperative infection, with an area under the curve of 0.742 (<i>p</i> = 0.001). When the RPUD cut-off value was accepted as 14, sensitivity was 0.613 and specificity was 0.779. <b><i>Conclusion:</i></b> This study showed a significant association between HU values in RPUD and the risk of infectious complications following RIRS. This finding suggests that incorporating urine HU values from CT images into preoperative risk assessment could be crucial for infection prevention and management.