THE ADDED VALUE OF C-REACTIVE PROTEIN IN DIAGNOSING PNEUMONIA IN PRIMARY CARE

Abstract Objectives. C-reactive protein (CRP) is increasingly used in the diagnostic work-up for community acquired pneumonia in primary care. The added diagnostic value of CRP beyond signs and symptoms however remains unclear. We aim to quantify the added value of CRP using individual patient data of multiple studies. Methods. Studies on diagnostic accuracy of CRP in adult outpatients with suspected lower respiratory tract infections were included in this individual patient data meta-analysis. The added value of CRP beyond a basic signs and symptoms prediction model was assessed based on improvement in discrimination and risk classification both within the individual studies as well as across studies. Results. Authors of 8 studies (n=5308) provided their datasets. In all datasets discrimination improved after adding CRP to the basic model, with a mean improvement in area under the ROC curve of 0.075 (range: 0.02-0.18). Overall the proportion of patients without pneumonia correctly classified as low risk increased from 28% to 36% when CRP was added. Furthermore, the proportion of patients with pneumonia assigned to the low risk category remained equal (n=4), the proportion of patients assigned to the intermediate category decreased from 56% to 51% and the proportion correctly classified as high risk increased from 63% to 70%. Conclusion. Adding CRP to the diagnostic workup of patients suspected of pneumonia in primary care improves their risk classification. However, even with CRP a substantial group will still be labelled as having intermediate risk of pneumonia, in which challenges in clinical decision making remain.