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-reactiv e protein (CRP) associated with clinically undetectable serious bacterial i nfection (SBI) in febrile children 1 to 36 months of age. Methods. Febrile children presenting to a pediatric emergency department (E D) with ages ranging from 1 to 36 months, temperatures greater than or equa l to 39 degreesC, 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 scal e were recorded at the time of the initial evaluation. The white blood cell count (WBC), band count, absolute neutrophil count (ANC), and CRP concentr ation 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 us ing antibiotics within 1 week of their presentation to the ED were excluded . The main outcome result was the presence of laboratory or radiographicall y proven SBI (bacteremia, meningitis, urinary tract infection, pneumonia, s eptic 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 te mperature, duration of fever, and Yale observation scale. CRP concentration , WBC, and ANC were significantly different between the 2 groups. In a mult ivariate logistic regression analysis, only CRP remained as a predictor of SBI (Beta = 0.76, 95% confidence interval [CI]: 0.64, 0.89). Receiver-opera ting 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 (AU C 0.805, SE 0.051, 95% CI: 0.705, 0.905) and to WBC (AUC 0.761, SE 0.068, 9 5% CI: 0.628, 0.895). A CRP cutoff point of 7 was determined to maximize bo th sensitivity and specificity (sensitivity 79%, specificity 91%, likelihoo d 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 concentrat ion 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 i n the evaluation of febrile young children who are at risk for occult bacte remia and SBI, with a better predictive value than the WBC or ANC.