Comparison of Procalcitonin With Commonly Used Biomarkers and Algorithms for Evaluating Suspected Pediatric Musculoskeletal Infection in the Emergency Department

Introduction: It is difficult to distinguish between children with infectious versus noninfectious conditions of the musculoskeletal system during initial evaluation. Clinical predictive algorithms potentially support this effort but not without limitations. Procalcitonin (PCT) has been proposed as a biomarker to help differentiate infection from noninfection. This study evaluates the adoption and utility of PCT during initial infection evaluations and assesses test characteristics of commonly used parameters and algorithms. Methods: PCT was introduced for initial laboratory evaluation of the suspected musculoskeletal infection. Prospective enrollment occurred from July 2020 to November 2021 with 3 cohorts established after a retrospective review of final diagnoses at the end of treatment: 1) deep infection, 2) superficial infection, and 3) noninfection. Univariate and multivariate logistic regression analysis of parameters and diagnoses was performed. Test characteristics of individual and aggregated parameters were assessed. Results: Among 258 children evaluated, 188 (72.9%) had PCT drawn during the evaluation. An increase of PCT acquisition from 67.8% to 82.4% occurred over the study timeframe. Eighty-five children were prospectively studied, including those with deep infection (n=21); superficial infection (n=10), and noninfection (n=54). Test characteristics of parameters showed accuracy ranging from 48.2% to 85.9%. PCT >0.1 ng/mL independently predicted deep infection in 84.7% of cases, outperforming white blood cell, C-reactive protein (CRP), and absolute neutrophil count. Using study thresholds for CRP, erythrocyte sedimentation rate, PCT, and Temp improved accuracy to 89.4%. Conclusions: PCT is a potentially useful biomarker during the initial assessment of children suspected to have a musculoskeletal infection. Systematic evaluation using a combination of parameters improves the accuracy of assessment and assists predictive judgment under uncertainty. PCT <0.1 ng/mL, erythrocyte sedimentation rate <18 mm/hr, CRP <3.3 mg/dL, and temperature <37.8°C should reasonably reassure clinicians that deep musculoskeletal infection is less likely, given the high negative predictive value and collective accuracy of these parameters. Level of Evidence: Level III - Retrospective cohort comparison.