Admission Neutrophil-to-Lymphocyte Ratio Is Superior to WBC Count at Predicting the Presence and Severity of Pediatric Musculoskeletal Infection.

Background: Accurately determining the presence and severity of pediatric musculoskeletal infection (MSKI) is crucial for effective triage and treatment. Although the white blood-cell (WBC) count is often used as a marker for MSKI, we hypothesized that the use of the WBC count is limited by age-related variability in children. We proposed that the absolute neutrophil-to-lymphocyte ratio (NLR), which has less age-related variability, is a more reliable indicator for both diagnosing and assessing the severity of MSKI. The present study aims to compare the utility of WBC against that of the NLR, as well as C-reactive protein (CRP) and erythrocyte sedimentation rate (ESR), for predicting MSKI presence and severity in children.

Methods: A retrospective cohort study was conducted with use of a database of pediatric orthopaedic consultations for suspected MSKI between January 2013 and July 2022. Diagnoses were categorized as MSKI or no infection, and the severity of any present infection was stratified as local or disseminated. Admission laboratory values were collected. Statistical modeling was performed to assess the capabilities of the WBC, NLR, CRP, and ESR to diagnose MSKI and to assess infection severity, with cutoff thresholds established for clinical use.

Results: This study included 650 patients (median age, 5.2 years; 63% male; 75% White). Of these, 247 patients had no infection, while 403 were diagnosed with an MSKI. Median WBC count, NLR, CRP, and ESR were all significantly higher in pediatric cases of confirmed MSKI. WBC was a poor predictor of infection severity, whereas NLR, CRP, and ESR each positively correlated with infection severity. At the time of admission, an NLR of 4 was highly specific for detecting the presence of infection, and an NLR of 5.8 was highly specific for predicting infection dissemination. CRP was the best predictor of both infection presence and severity, demonstrating the highest specificity and sensitivity, followed by NLR, which outperformed ESR and WBC.

Conclusions: Because of considerable age-related variability, the predictive value of the WBC count for pediatric MSKI presence and severity is limited. NLR, which is less affected by age-related variability, is superior at predicting MSKI severity. Although CRP remains the benchmark, the NLR offers a valuable alternative to the WBC. Our study provides a comparative framework for these biomarkers, enhancing MSKI assessment across various clinical settings.

Level of evidence: Diagnostic Level III . See Instructions for Authors for a complete description of levels of evidence.