The Use of Serum Procalcitonin in the Setting of Infected Ureteral Stones: A Prospective Observational Study

Infected ureteral stones are a urologic emergency and require urgent decompression. We set out to determine whether serum procalcitonin (PCT) could aid in the diagnosis of infected ureteral stones. All consecutive patients presenting to the emergency room from November 9, 2016, to November 10, 2018, with an obstructing ureteral stone were included. All patients had complete blood count, urinalysis (UA), PCT, and urine culture (UCx). Subgroup analysis was performed in a "clinically equivocal" cohort of afebrile patients defined as a leukocytosis >10⁴/μL and UA with <50 white blood cells (WBCs) per high powered field (hpf). Patients with positive and negative UCx were compared. A total of 231 patients were included, of whom 56 had a positive UCx. Of all covariates, UA WBCs with a cutoff of 9 per hpf performed best at predicting positive UCx with an area under the curve (AUC) of 0.87. PCT did not perform as well with an ideal cutoff of 0.08 ng/mL, having an AUC of 0.77, sensitivity 70.6%, specificity 73.9%, positive predictive value (PPV) 34.3%, and negative predictive value (NPV) 92.9%. When looking at the clinically equivocal cohort, UA WBCs with a cutoff of 6 per hpf appeared to perform best at predicting a positive UCx with an AUC of 0.72. PCT was less predictive in this cohort with an ideal cutoff of 0.3 ng/mL, having an AUC of 0.32, sensitivity 47.1%, specificity 85.2%, PPV 38.1%, and NPV 89.3%. PCT does not appear to be a superior marker for diagnosing urinary tract infection in the setting of obstructing ureterolithiasis when compared with components of the standard work-up.