Diagnostic Value of IL-6, CRP, WBC, and Absolute Neutrophil Count to Predict Serious Bacterial Infection in Febrile Infants

Since clinical manifestations of most febrile infants younger than three months old are nonspecific, differentiation of Serious Bacterial Infection (SBI) from self-limiting viral illness is a significant challenge for pediatricians. This study was performed to assess the diagnostic value of white blood cell count (WBC), Absolute Neutrophil Count (ANC), Interleukin -6 (IL-6) and C-reactive protein (CRP) level to predict SBI in febrile infants younger than three months old who were hospitalized. This was a diagnostic test validation study. In this prospective study, 195 febrile infants admitted to 17 Shahrivar Hospital underwent a full sepsis workup including blood, urine, cerebrospinal fluid cultures and chest radiography. WBC count, ANC and CRP and Il-6 level were measured in all patients. Serum IL-6 concentration was measured by Enzyme-linked Immunosorbent Assay test. Then diagnostic, values of these tests for predicting SBI was compared with each other. Of total cases, 112 (57.4%) infants were male. SBI was diagnosed in 29 (14.9%) patients. The most common type of SBI was Urinary Tract Infection (UTI). Serum IL-6 (³20pg/dl) had sensitivity, specificity, positive predictive value (PPV) and negative predictive value (NPV) of 79/1%, 91.6%, 75.4%, 60.3%, respectively and for CRP (³ 10mg/l) values were 81.6%, 89.8%, 78.2%, and 52%, respectively. The predictive values of CRP and IL-6 were higher than WBC and ANC. IL-6 and CRP are more valid and better diagnostic markers for predicting SBI than WBC count and ANC. CRP level seems to be an accessible and cost-effective marker for early diagnosis of SBI. Since by no marker we can totally rule out SBI in febrile infants < three months of age, it is recommended to administer systemic antibiotics until culture results become available.