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Table 2 Guidance on interpreting C-reactive protein (CRP) results

From: General practitioner use of a C-reactive protein point-of-care test to help target antibiotic prescribing in patients with acute exacerbations of chronic obstructive pulmonary disease (the PACE study): study protocol for a randomised controlled trial

CRP guidance:
The decision to prescribe antibiotics or not has to be based on a comprehensive assessment of the likely risks and benefits given:
 • The patient’s underlying health status (chronic obstructive pulmonary disease (COPD) severity, comorbidities, frailty)
 • Clinical features of the current exacerbation
Measurement of CRP can aid decision-making but is not meant to replace clinical assessment.
Patients with the following features are likely to be at increased risk of complications:
 • Severe COPD (GOLD grade III)
 • Past history of severe exacerbations (requiring hospitalisation)
 • Significant comorbidities (e.g. heart failure, poorly controlled diabetes, lung cancer)
Sputum purulence is currently the best clinical predictor of bacterial infection. However:
 • Patient-reported sputum colour is generally not reliable
 • Purulence can be increased in viral infections as well as bacterial infections
 • Try and obtain a sputum sample in order to objectively assess sputum purulence where possible
 • Ask the patient how much the colour of their sputum has changed from its usual colour. This is particularly pertinent when it is not possible to objectively assess their sputum
CRP measurement:
CRP < 20 Antibiotics are unlikely to be beneficial and usually should not be prescribed
CRP 20–40 Antibiotics may be beneficial – mainly if purulent sputum is present. You may decide to prescribe antibiotics after taking into account the patient’s underlying health status and the features of the current exacerbation
CRP > 40 Antibiotics are likely to be beneficial. Consider prescribing antibiotics unless the patient is assessed as being at lower risk of complications and unlikely to have a bacterial infection (no increased sputum purulence and no features suggesting severe exacerbation)