Diagnostic use of C-reactive protein in bacteraemic emergency department patients

To assess C-reactive protein (CRP) as a marker of bacteraemia in ED patients.

A retrospective review of a convenience sample of adult patients was conducted at an urban, tertiary care, academic ED. Patients were included in the present study if they had CRP and blood cultures taken during their ED assessment. Neutropenic patients were excluded. Sensitivity, specificity, predictive values and likelihood ratios for CRP in the detection of bacteraemia were calculated.

Over a 12 month period 1214 patients were included in the present study. Blood cultures were positive in 77 (6.3%, 95% confidence interval [CI] 5.0-7.6%), and contaminated in 33 (2.7%, 95% CI 1.8-3.6%). An elevated CRP was 94% sensitive (95% CI 86-98%) and 18% specific (95% CI 16-20%) for concurrent bacteraemia. The positive likelihood ratio for bacteraemia with an elevated CRP was 1.15 (95% CI 1.07-1.23), and the negative likelihood ratio was 0.33 (95% CI 0.23-0.49).

Although the present study has limitations, it appears to show that CRP has limited diagnostic utility for the detection of bacteraemia in ED patients.