LAUSR

Objectives The aim of the study was to investigate the diagnostic efficacy of C-reactive protein (CRP) in predicting serious bacterial infection (SBI) in febrile children aged 3 to 36 months with extreme leukocytosis (EL), defined as a peripheral white blood cell count of 25,000 to 49,999/mm3. Methods The presence of SBI was reviewed in previously healthy children aged 3 to 36 months with a fever of 39°C or higher and EL, who visited a tertiary care hospital emergency department between September 2010 and August 2015. We measured cutoff values of CRP with corresponding likelihood ratios (LRs) and posttest probabilities (PPs). Results Of 9989 febrile children, 4252 (42.6%) underwent assays for white blood cell and CRP. Of 233 (5.5%) children with EL, 133 (3.1%) were enrolled, of whom 43 (32.3%; 95% confidence interval [CI], 25.0%–40.7%) had SBI, including 33 pyelonephritis, 5 deep abscesses, 3 lobar pneumonia, and 2 soft tissue infections. With the cutoff of 7.8 mg/dL, the sensitivity of CRP in predicting SBI was 81.4% (95% CI, 67.4%–90.3%); the specificity, 80.0% (95% CI, 70.6%–87.0%); the positive predictive value, 66.0% (95% CI, 52.6%–77.3%); the negative predictive value, 90.0% (95% CI, 81.5%–94.9%); the positive LR, 4.1; and the PP, 66.0% (95% CI, 55.6%–75.0%). A CRP concentration of 16.1 mg/dL or higher yielded an LR of 11.2 and a PP of 84.2% (95% CI, 62.1%–94.5%). A CRP concentration of lower than 3.4 mg/dL yielded an LR of 0.05 and a PP of 2.4% (95% CI, 0.3%–14.6%). Conclusions High concentration of CRP is strongly associated with the presence of SBI in febrile children with EL.