Stone-induced obstructive pyelonephritis (siOPN) is a critical urological emergency that carries a high risk of rapid clinical deterioration. This study aimed to evaluate the predictive performance of the Systemic Inflammatory Response Syndrome (SIRS) criteria, the Modified Early Warning Score (MEWS), and the National Early Warning Score (NEWS) in identifying patients with siOPN who are at risk for intensive care unit (ICU) admission. This retrospective cohort study included 175 patients with radiologically confirmed siOPN. SIRS, MEWS, and NEWS scores were calculated at admission. Predictive accuracy was assessed via ROC analysis, with pairwise AUC comparisons performed using DeLong’s test. Seventeen patients (9.7%) required ICU admission. Female sex was significantly more prevalent in the ICU group (82.4% vs. 48.1%, p = 0.007). ICU patients had lower Hounsfield Unit values (p = 0.017), and higher C-reactive protein (CRP) (p = 0.001) and Neutrophil-to-lymphocyte ratio (NLR) (p = 0.002) levels. All three early warning scores were significantly higher in the ICU cohort (p < 0.001). NEWS had the highest predictive accuracy (AUC: 0.993), outperforming MEWS (0.978) and SIRS (0.974; both p < 0.001). CRP and NLR showed modest performance (AUCs: 0.751 and 0.730). Negative predictive values (NPV) were highest for NEWS (99.3%), though positive predictive values were generally low. NEWS demonstrated the highest discriminative performance for predicting ICU admission to patients with siOPN. Female sex was associated with increased ICU admission risk, although this finding should be interpreted with caution. Given its high NPV and ease of use, NEWS may be a useful screening tool for triage in emergency urological settings. Further prospective validation is warranted.