Upper Urinary Tract Culture Positivity in Obstructive Ureterolithiasis—Clinical Severity, Inflammatory Biomarkers, and Early Risk Assessment

Background/Objectives: Obstructive ureterolithiasis complicated by infection may progress rapidly to systemic deterioration, while microbiological confirmation is generally unavailable during initial assessment. This study evaluated the association of admission procalcitonin (PCT), National Early Warning Score 2 (NEWS2), and routine urinary parameters with positive upper urinary tract culture in patients requiring urgent urinary decompression. Methods: This retrospective single-center observational study included 240 adults admitted with obstructive ureterolithiasis who underwent upper urinary tract decompression by ureteral stenting or percutaneous nephrostomy. Demographic, clinical, laboratory, and urinary parameters obtained at admission were compared according to upper urinary tract culture status. Factors associated with culture positivity were assessed using univariable and multivariable logistic regression. Four clinically defined models were compared: a reference model containing WBC, CRP, urinary nitrites, and proteinuria; models separately adding PCT or NEWS2; and a complete model containing both. Discrimination was compared using AUCs and the DeLong test, while model fit was assessed using likelihood-ratio tests. Internal validation was performed using 1000 bootstrap resamples. Results: Positive upper urinary tract cultures were identified in 86 patients (35.8%). In the complete model, PCT per doubling (aOR 1.820; 95% CI 1.502–2.205; p < 0.001) and NEWS2 (aOR 1.167; 95% CI 1.014–1.344; p = 0.031) remained independently associated with culture positivity. The reference model had an AUC of 0.691. Adding PCT increased the AUC to 0.831 (ΔAUC 0.140; p < 0.001), whereas adding NEWS2 alone resulted in an AUC of 0.720 (ΔAUC 0.029; p = 0.085). The complete model achieved an apparent AUC of 0.839 and an optimism-corrected AUC of 0.821. After PCT was included, NEWS2 improved overall model fit (p = 0.029) and produced an additional increase in AUC (ΔAUC 0.007; p = 0.448). Conclusions: Admission PCT and NEWS2 were independently associated with positive upper urinary tract culture The combined model showed good discrimination, although external validation is required before clinical application. Urinary nitrite positivity retained an independent association only in the exploratory cut-off-based analysis.