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Biological markers for predicting bacterial infection, bacteremia, and severity of infection in the emergency department

Tudela P, Prat C, Lacoma A, Mòdol Deltell JM, Domínguez J, Giménez M, Tor J

Unitat de Curta Estada-Urgències, Servei de Microbiologia, Servei de Medicina Interna, Hospital Universitari Germans Trias i Pujol, Fundació Institut d’Investigació en Ciències de la Salut Germans Trias i Pujol, Universitat Autonòma de Barcelona, Badalona, Barcelona, Spain. CIBER Enfermedades Respiratorias, Instituto de Salud Carlos III, Barcelona, Spain.

Objectives: To analyze the utility of using clinical and laboratory variables (C-reactive
protein [CRP], procalcitonin [PCT], proadrenomedullin [proADM] and neopterin
concentrations) as predictors in cases of bacterial infection in an emergency department.
Methods: The patients were enrolled from the emergency department when blood was
extracted for culture. We recorded age; sex; Charlson index, white blood cell count,
presence of band cells, neutrophil count, microbiology findings and CRP, PCT, proADM,
and neopterin concentrations. Severity of infection was defined by a patientÂ’s admission
to the intensive care unit, death, or emergency surgery. The data were analyzed by
univariate and multivariate analyses; the area under the receiver operating characteristic
curve and diagnostic yield were calculated for each variable.
Results: We included 412 patients with bacterial infection confirmed by microbiology
(28.3%), possible infection not confirmed by microbiology (39.3%), fever of unknown
origin (9.9%), and no bacterial infection (22.3%). Blood cultures were positive in 53
(12.8%) and 34 infections (8.2%) were considered severe. The independent predictors
of bacterial infection were CRP  70 mg/L, PCT  0.4 ng/mL, and presence of band
cells, although diagnostic precision was limited. The independent variables that best
predicted bacteremia were PCT > 1 ng/mL and proADM > 2 nmol/L; these variables had
negative predictive values of 94% and 93%, respectively. The variables that predicted
severity of infection were PCT > 1 ng/mL and proADM > 1.94 nmol/L, which both had
negative predictive values around 96%.
Conclusions: CRP and PCT concentrations and the presence of band cells can suggest
bacterial infection in emergency patients, although the diagnostic value of these markers
is limited. However, the diagnostic yields are high for PCT and proADM concentrations
and these measurements can be useful for ruling out bacteremia and severity of

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