Systemic Immune-Inflammation Index and Neutrophil-to-Platelet Ratio as Predictors of Intensive Care Requirement and Hospital Stay in Acute Obstructive Pyelonephritis Requiring Percutaneous Nephrostomy.

PURPOSE: There is a growing need for rapid, simple, and cost-effective biomarkers that facilitate early risk stratification in patients with severe upper urinary tract infections. This study aimed to investigate whether the systemic immune-inflammation index (SII) and neutrophil-to-platelet ratio (NPR) at hospital admission can predict the need for intensive care unit (ICU) admission and the duration of hospitalization in patients with acute obstructive pyelonephritis managed with percutaneous nephrostomy. MATERIALS AND METHODS: Patients aged ≥18 years who were hospitalized with acute obstructive pyelonephritis and underwent emergency percutaneous nephrostomy between June 19, 2020, and July 30, 2025, were evaluated retrospectively. A comparative analysis was conducted between patients who required ICU admission and those who did not. Admission SII and NPR were calculated, and their associations with ICU requirement and length of hospital stay were analyzed using multivariable logistic and linear regression models, receiver operating characteristic curves, and the Youden index. RESULTS: A total of 440 patients were analyzed, of whom 29 required ICU care. Patients requiring ICU admission exhibited significantly higher median SII, NPR, leukocyte counts, neutrophil counts, and procalcitonin levels, along with lower hemoglobin and lymphocyte concentrations. In multivariable logistic regression adjusted for class imbalance, elevated SII independently predicted ICU admission (odds ratio, 1.70; 95% confidence interval, 1.34-2.17; P < .001). Admission SII was positively associated with the duration of hospital stay (β = 0.184; P < .001). CONCLUSION: SII represents an accessible, cost-effective biomarker for early identification of patients at heightened risk of clinical deterioration requiring ICU transfer and prolonged hospitalization in acute obstructive pyelonephritis.