Evaluating the evidence for the implementation of C-reactive protein measurement in adult patients with suspected lower respiratory tract infection in primary care: a systematic review.

Background: Excessive prescription of antibiotics in patients with lower respiratory tract infection (LRTI) is common in primary care and might be reduced by rapid point-of-care (POC) C-reactive protein (CRP) testing. However, the exact benefits of this test are unclear.

Objective: To review the available evidence for the role of POC CRP measurement in (i) guiding antibiotic prescription, (ii) predicting aetiology, (iii) prognosis and (iv) diagnosis (pneumonia) in LRTI patients.

Methods: For each research question, studies were retrieved through an electronic literature search in Medline, Embase and the Cochrane Library using synonyms for CRP and LRTI combined with different relevant subheadings. Study quality was assessed using validated instruments and predefined outcome measures were extracted from each study.

Results: The search yielded 13 articles, each answering one or more questions; one was excluded by insufficient internal validity. (i) One of four studies showed a significant reduction in the antibiotic prescriptions when applying POC CRP measurement [relative risk (RR) 0.6, 95% confidence interval (CI) 0.5-0.7]. (ii) Three studies on aetiology demonstrated that an elevated CRP was associated with bacterial [odds ratio (OR) 2.46-4.8] and one with viral (OR 2.7) aetiology. (iii) Results on the prognostic value were contradictory, providing evidence for faster symptom resolution (RR 1.16, 95% CI 1.1-1.3), higher mortality rate (RR 2.5, 95% CI 1.2-5.1) and no difference in outcome in patients with high CRP levels. (iv) Four studies showed that CRP had limited value as a single predictor of pneumonia. When combined with clinical assessment, its value increased according to two of these studies (receiver operating characteristic area from 0.7 to 0.9). However, methodological flaws and/or wide CIs limit the generalizability of findings in all studies.

Conclusion: The evidence for the benefits of POC CRP measurement in LRTI patients in primary care is limited, contradictory and does not support its use to guide treatment decisions yet.