Utility of interleukin‐6 to identify serious bacterial infections in febrile infants aged ≤60 days

Abstract Aim The aim of this study is to investigate the utility of interleukin‐6 (IL‐6) in the early diagnosis of serious bacterial infections (SBI) in febrile infants and to compare it with C‐reactive protein (CRP). Methods Retrospective study conducted in the paediatric emergency department in Gothenburg, Sweden, on previously healthy, full‐term infants aged ≤60 days with fever without a source (FWS) from 2014 to 2017. Results We included 536 infants with FWS, of whom IL‐6 was analysed in 364 (68%) and CRP was analysed in 494 (92%). Approximately 70% of the infants presented with a fever duration of less than 12 h. The prevalence of SBIs was 14.8% (95% CI,11.3–18.9) in the IL‐6 group and 17.8% (95% CI,14.5–21.5) in the CRP group. The sensitivity, specificity, negative predictive value (NPV), and positive predictive value (PPV) of IL‐6 ≥50 ng/L were 93%, 66%, 98% and 33%, respectively. For CRP ≥20 mg/L, the sensitivity, specificity, NPV, and PPV were 76%, 89%, 95%, and 55%, respectively. Logistic regression analysis showed that CRP was significantly associated with SBI ( p < 0.0001) in the entire population, whereas IL‐6 was not. Conclusion Interleukin‐6 showed high sensitivity and NPV, which might assist in identifying SBIs early in febrile infants. However, IL‐6 was not shown to be superior to CRP and further studies are needed to investigate whether IL‐6 should be incorporated in clinical management.