Bacteraemia prediction in emergency medical admissions: role of C reactive protein.

AIM To define the contribution made by C reactive protein (CRP) measurement to bacteraemia prediction in adults with medical emergencies in the UK. METHODS This two year cohort study involved 6234 patients admitted as emergency cases to the acute medical or infectious diseases services of the Oxford Radcliffe Hospitals, in whom blood cultures were taken on arrival. The main outcome measures were bacteraemia risk associated with admission CRP concentrations, lymphocyte counts, and neutrophil counts. RESULTS The quantitative associations between CRP concentration, admission lymphocyte count, and neutrophil count were defined. Risk of bacteraemia rose continuously as the CRP increased: no "cutoff" value was evident. Models examining combinations of CRP, neutrophil count, and lymphocyte count were developed and validated using a split sample technique. CRP contributed to a model including lymphocyte and neutrophil counts, but its effect was small. CRP alone performed no better than either a model combining lymphopenia and neutrophilia, or than lymphopenia alone. CONCLUSIONS In patients with acute medical emergencies who are suspected of bacteraemia clinically, CRP concentrations, although associated with bacteraemia, have a limited role in bacteraemia prediction.