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

Abstract

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.

Figures

Figure 1

This figure illustrates the performance, in the validation of models built using C reactive protein (CRP) concentration, lymphocyte count (LC), and neutrophil count (NP). (A) Receiver operator characteristic (ROC) curves for models built using CRP concentration, lymphocyte count, and neutrophil count (CRP, LC, NP), lymphocyte and neutrophil counts (NP, LC), or single variables. (B) Areas under the ROC curves. (C) The significance of pairwise comparisons between the areas.

Figure 2

The observed likelihood ratios for bacteraemia associated with the parameters shown in fig 1. (A) The likelihood ratios associated with probabilities of bacteraemia calculated by models without (plus symbols) or with (dots) C reactive protein (CRP). (B–D) Likelihood ratios produced by the range of neutrophil counts, CRP measurements, and lymphocyte counts, respectively.