A Serum C-Reactive Protein and Procalcitonin-Based Risk Score to Predict Urinary Infection in Patients with Obstructive Urolithiasis Undergoing Decompression

OBJECTIVE To develop a risk score utilizing CRP and procalcitonin to better predict a clinical infection for patients with obstructive urolithiasis. METHODS A retrospective review was performed of patients presenting to the emergency room from December 2017 to February 2019 who underwent upper urinary tract decompression due to concern for infection in the setting of obstructing urolithiasis. Over 30 clinical parameters were assessed and a composite risk score was created. Univariate and multivariate forward stepwise regression were performed to identify predictors of true UTI. RESULTS 98 patients met inclusion criteria, of which a true UTI was identified in 50 (51%). The standard model of serum WBC>15 or temperature>38°C had an AUC of only 0.67 to predict UTI. A multivariable regression-based 4-point risk score (1-point for each of the following: positive urinary gram stain, perinephric fat stranding on CT, serum C-reactive protein >21.95, and serum procalcitonin >0.36) had an AUC of 0.91 to predict UTI. Individually, these components had AUC of 0.68, 0.68, 0.80, and 0.77, respectively. The chances of confirmed UTI were 8%, 11%, 68%, and 100% for risk scores of 0, 1, 2, and 3-4 respectively (p<0.001). CONCLUSIONS Only 50% of patients with a suspected UTI and an obstructing stone were ultimately confirmed to have a UTI. A risk score consisting of gram stain, perinephric fat stranding, CRP, and PCT can improve UTI prediction and warrants further study.