Presentation Authors: Madeleine Manka*, Kevin Wymer, Vidit Sharma, Nicole Dodge, Deepak Agarwal, Matthew Gettman, Marcelino Rivera, Rochester, MN
Introduction: Identifying patients with an obstructing stone and underlying urinary tract infection (UTI) can be challenging as urinary cultures often take 24-48 hours to result and factors such as age and comorbidities may alter clinical symptoms. Additionally, a complete obstruction may mask infected urinalyses. Herein we evaluate the utility of conventional clinical predictors of UTI in the presence of an obstructing stone and compare them to a data-derived UTI risk score.
Methods: A retrospective review was performed of patients presenting to the emergency room from December 2017 to October 2018 with obstructing urolithiasis and clinical concern for infection evaluated for stent / nephrostomy tube decompression. A true UTI was defined as any of the following: gross purulence proximal to the stone or positive catheterized bladder, renal pelvic, or blood cultures. Over 30 demographic, symptom, comorbidity, laboratory, and radiographic parameters were tested on univariable analyses to determine association with infection. A composite risk score was created using retained factors in stepwise multivariable logistic regression modeling.
Results: A cohort of 74 patients was identified with obstructive urolithiasis evaluated for decompression due to concern for UTI of whom only 37 (50%) had a true UTI. The standard model of serum WBC > 15 or temperature > 38Â°C had an AUC of only 0.68 to predict true UTI. Conversely, a data-derived 5-point risk score (1-point for each of the following: positive gram stain, >50 WBCs/hpf on urine microscopy, perinephric fat stranding on CT, serum C-reactive protein (CRP) > 21.95, and serum procalcitonin (PCT) > 0.36) had an AUC of 0.92 (Figure). The chances of a true UTI increased from 5% to 60% to 93% among patients with risk scores of 0-1, 2, and 3-5, respectively (p < 0.001).
Conclusions: Currently, only 50% of patients with a suspected UTI and an obstructing stone are ultimately found to have a true UTI. A risk score (consisting of gram stain, pyuria, perinephric fat stranding, CRP, and PCT) outperformed standard clinical variables in predicting a true UTI in patients with obstructing urolithiasis. We are currently validating this score to help elucidate which patients with obstruction and clinical suspicion for infection require decompression.