C-reactive protein in febrile children 1 to 36 months of age with clinically undetectable serious bacterial infection.

OBJECTIVE To determine the diagnostic properties of quantitative C-reactive protein (CRP) associated with clinically undetectable serious bacterial infection (SBI) in febrile children 1 to 36 months of age. METHODS Febrile children presenting to a pediatric emergency department (ED) with ages ranging from 1 to 36 months, temperatures > or =39 degrees C, and clinically undetectable source of fever were enrolled in this prospective cohort study. Demographic information, ED temperature, duration of fever, and clinical evaluation using the Yale observation scale were recorded at the time of the initial evaluation. The white blood cell count (WBC), band count, absolute neutrophil count (ANC), and CRP concentration were measured at the same time. All patients received blood cultures and either a screening urinalysis or urine culture. A chest radiograph was obtained at the discretion of the ED physician. Patients with history of using antibiotics within 1 week of their presentation to the ED were excluded. The main outcome result was the presence of laboratory or radiographically proven SBI (bacteremia, meningitis, urinary tract infection, pneumonia, septic arthritis, and osteomyelitis). RESULTS Seventy-seven patients were enrolled in the study. Fourteen (18%) had a SBI (6 urinary tract infection; 4 pneumonia, including 1 patient with Streptococcus pneumoniae bacteremia; and 4 occult S pneumoniae bacteremia), and 63 had no SBI. The 2 groups were indistinguishable in age, sex, ED temperature, duration of fever, and Yale observation scale. CRP concentration, WBC, and ANC were significantly different between the 2 groups. In a multivariate logistic regression analysis, only CRP remained as a predictor of SBI (Beta = 0.76, 95% confidence interval [CI]: 0.64, 0.89). Receiver-operating characteristic analysis demonstrated CRP (area under curve [AUC] 0.905, standard error [SE] 0.05, 95% CI: 0.808, 1.002) to be superior to ANC (AUC 0.805, SE 0.051, 95% CI: 0.705, 0.905) and to WBC (AUC 0.761, SE 0.068, 95% CI: 0.628, 0.895). A CRP cutoff point of 7 was determined to maximize both sensitivity and specificity (sensitivity 79%, specificity 91%, likelihood ratio 8.3, 95% CI: 3.8, 27.3). Multilevel likelihood ratios and posttest probabilities were calculated for a variety of CRP levels. A CRP concentration of <5 mg/dL effectively ruled out SBI (likelihood ratio 0.087, 95% CI: 0.02, 0.38, posttest probability of SBI 1.9%). CONCLUSIONS Quantitative CRP concentration is a valuable laboratory test in the evaluation of febrile young children who are at risk for occult bacteremia and SBI, with a better predictive value than the WBC or ANC.