Evaluation of the Diagnostic Value of Neutrophil-to-lymphocyte Count Ratio (NLR) and Platelet-to-lymphocyte Ratio (PLR) for Identifying Serious Infection (SI) and Serious Bacterial Infection (SBI) in Febrile Young Infants < 90 Days Old

Abstract Background:Neutrophil-to-lymphocyte ratio (NLR) and platelet-to-lymphocyte ratio (PLR) are simple and easy to calculate biomarkers. They have been reported as a predictor of severity and prognosis in adult patients with bacteremia. However, there is a paucity of literature examining the use of NLR and PLR as a diagnostic biomarker in pediatrics. This study aims to evaluate the diagnostic value of the NLR and PLR for identifying serious infections (SI) and serious bacterial infections (SBI) in febrile young infants <90 days old. Methods: A retrospective review of neonates and infants who were admitted for evaluation of fever between 1st July 2018 and 31st December 2018 were reviewed retrospectively. Patients aged less than 90 days of life admitted for fever from the emergency department were included. Patient age, gender, comorbidities, body temperature, clinical findings and initial laboratory results including white blood cell (WBC) count, NLR, PLR, serum levels of C-Reactive Protein (CRP) were assessed, and the microbiological investigations and final clinical diagnoses were evaluated. Results: There were 561 patients identified for inclusion. SI and SBI were diagnosed in 166 (29.6%) and 98 (17.5%) patients. Mean absolute neutrophil count, NLR were significantly higher in the SI group compared to the non-SI group (1.39±1.04 vs 1.09±0.87, p=0.001). The NLR was also significantly different in the SBI compared to the non-SBI group (1.38±0.88 vs 1.13±0.94, p=0.019). PLR did not show statistical significance in differentiating SI or SBI from non SI or SBI group. For SI and SBI, the area under the Receiver Operating Characteristic (AUROC) curve value of NLR was 0.57 (95 % CI 0.46-0.69) and 0.61 (95% CI 0.48-0.73), respectively. Although we found significantly higher NLR values in infants with SI and SBI, our results indicate that CRP was more accurate at detecting SI and SBI. Conclusion: Our study provided initial evidence on the use of the NLR in combination with other biomarkers in the diagnosis of serious infection and serious bacterial infection in young infants < 90 days’ of life. Prospective evaluation of this finding is needed to assess further its clinical value in the evaluation of young febrile infants for SI and SBI.