Reduction of unnecessary antibiotic therapy in newborn infants using interleukin-8 and C-reactive protein as markers of bacterial infections

Objective. To examine whether the determination of interleukin 8 (IL-8) and C-reactive protein (CRP) in neonates with suspected nosocomial bacterial i nfection (NBI) is feasible and cost-effective in reducing antibiotic therap y. Methods. Between April 1996 and May 1997, IL-8 was measured 260 times along with blood cultures, CRP, and immature-to-total-neutrophil (IT) ratio for suspected NBI in term and preterm neonates. All infants were retrospectivel y analyzed for NBI. Sensitivity, specificity, positive and negative predict ive values, and 95% confidence intervals were calculated for IL-8, CRP, and IT ratio. Receiver-operating characteristic curves were analyzed to determ ine optimal thresholds. Between June 1997 and June 1998, IL-8 was measured 215 times in newborn infants with suspected NBI and the decision to start a ntibiotic therapy was based on increased IL-8 and/ or CRP values. A cost-ef fectiveness analysis was performed and sensitivity, specificity, and receiv er-operating characteristic curves were reevaluated. Results. At the first suspicion of NBI, the combination of IL-8 greater tha n or equal to 53 pg/mL and/or CRP >10 mg/L detected culture-proven NBI with 96% sensitivity. The combined culture-proven and clinical NBI were detecte d with 93% sensitivity and 80% specificity. The use of IL-8 reduced unneces sary antibiotic therapy for suspected NBI by 73% and was cost-effective whe n compared with initiating antibiotic therapy based on clinical signs alone or based on clinical signs and an increased IT ratio and/ or CRP. Conclusions. The combination of IL-8 and/ or CRP is a reliable and early te st for the diagnosis of NBI in newborn infants. Using the combination of IL -8 and/or CRP to restrict antibiotic therapy to truly infected infants redu ces unnecessary antibiotic therapy and is cost-effective.