Comparison of procalcitonin with interleukin 8, C-reactive protein and differential white blood cell count for the early diagnosis of bacterial infections in newborn infants

Objective. To evaluate procalcitonin (PCT) as a test for early diagnosis of bacterial infections (BI) in newborn infants and to compare the results of PCT with those of interleukin 8 (IL-8), C-reactive protein (CRP) and differential white blood cell count. Study design. PCT was prospectively measured along with IL-8, CRP and differential white blood cell counts and blood cultures in 197 newborn infants at the first suspicion of bacterial infection. PCT, IL-8, CRP and differential white blood cell counts were analyzed for sensitivity, specificity and positive and negative predictive values after receiver operating characteristic curve analysis for best thresholds. The kinetics of PCT was determined in infants with and without BI. Results. Forty-six infants were diagnosed clinically as having BI, of whom 9 had BI with positive blood cultures. At a cutoff value of 0.50 mu g/l, PCT detected combined culture-proved and clinical BI with a sensitivity of 57% (95% confidence interval, 41%, 71%) and a specificity of 66% (95% confidence interval, 57%, 74%). The combination of IL-8 greater than or equal to 70 ng/l and/or CRP >10 mg/l achieved a sensitivity of 91% (95% confidence interval, 79%, 98%) and a specificity of 73% (95% confidence interval, 64%, 81%). PCT values of infected and not infected infants tended to rise for 24 h after initial evaluation and then decreased. Conclusion. The combination of IL-8 and CRP is more reliable than PCT as a test for early diagnosis of BI in newborn infants.