Is point-of-care CRP testing useful in guiding antibiotic prescribing in patients with respiratory tract infections?

Everyday throughout New Zealand, multiple patients will present to general practice with symptoms of a respiratory tract infection (RTI). A RTI can be caused by a number of different pathogens and prescribers are regularly faced with the question: “Is this RTI self-limiting and/or of viral origin or will this patient benefit from antibiotics?” The desire not to miss a diagnosis of pneumonia often leads to excessive prescribing of antibiotics for patients with symptoms of a lower RTI, e.g. a productive cough and chest signs.

To improve clinician’s ability to accurately diagnose pneumonia, interest is growing in the use of point-of-care C-reactive protein (CRP) testing devices, which are now available in New Zealand. Evidence suggests that with appropriate training, point-of-care CRP testing in patients with a RTI can reduce unnecessary antibiotic prescribing in two specific clinical scenarios:

1. Identifying patients with symptoms of a lower RTI who are unlikely to have pneumonia, i.e. where an antibiotic is not appropriate
2. Providing patients with an upper RTI who are convinced they “need” an antibiotic with reassurance that a prescription for an antibiotic is unlikely to be beneficial

Elevated CRP is a marker for bacterial infection and other pathological processes

Serum CRP is an acute phase marker for a number of pathological processes, including infection, inflammation, trauma or infarction.¹ The serum CRP level in a “healthy” person is usually less than 5 mg/L; this will begin to rise four to eight hours after tissue is damaged, peak within 24 – 72 hours, and return to normal two to three days after the pathological process has ceased.¹ Bacterial infections of the respiratory tract generally cause a greater CRP elevation than viral infections.

Health professionals in primary care who are appropriately trained in the use of the point-of-care device can obtain CRP results that, for the purposes of testing a patient with a RTI, are comparable to conventional laboratory testing (see: “Point-of-care CRP testing is rapid but is it accurate?”). Point-of-care testing has the advantage of being able to provide the clinician with a CRP result immediately, which can be factored into treatment decisions.

Point-of-care CRP testing may be useful for “ruling out” pneumonia in patients with lower RTI symptoms

Point-of-care CRP testing may help reduce unnecessary antibiotic prescribing for patients with a viral lower RTI by providing the clinician with increased confidence that the patient does not have pneumonia.

In December 2014, the United Kingdom National Institute for Health and Care Excellence (NICE) released guidelines recommending that point-of-care CRP testing may be useful to guide antibiotic prescribing for patients without a clinical diagnosis of pneumonia but with symptoms of a lower RTI, e.g. cough and at least one of: fever, sputum production, wheeze, or chest discomfort. NICE recommended that in this clinical situation:²

• Antibiotic treatment should not be routinely offered to patients if their CRP level is < 20 mg/L, as they are unlikely to have pneumonia
• Antibiotic treatment should be routinely offered to patients with symptoms of a lower RTI and a CRP level > 100 mg/L, as they are more likely to have pneumonia, assuming no underlying condition such as malignancy or autoimmune disease is present

In patients with symptoms of a lower RTI of uncertain origin and a CRP level between 20 – 100 mg/L the need for antibiotics remains reliant on clinical judgment. Factors such as co-morbidities, history of previous pneumonia and personal circumstances, e.g. living alone, may take on added significance when considering whether to prescribe an antibiotic. In patients in whom the consequences of pneumonia could be more severe, a prescription for an antibiotic at the initial consultation may be a reasonable strategy, while in lower risk patients a delayed prescription may be considered, i.e. to be collected/filled if symptoms do not resolve after several days.

For further information see: “ Delayed prescriptions for respiratory tract infections”

Point-of-care CRP testing when symptoms suggest an upper RTI

In patients with symptoms of an upper RTI, e.g. dry cough, pharyngitis, rhinitis, sneezing, the value of point-of-care CRP testing is in helping to reassure patients that they do not require an antibiotic, if the CRP result supports this judgement. A CRP level < 10 mg/L suggests that a patient does not have a bacterial infection and therefore a prescription for an antibiotic is likely to do more harm than good,¹ i.e. the potential adverse effects of the antibiotic outweigh any clinical benefits (which would be negligible in most cases).

Point-of-care CRP testing has been shown to reduce initial antibiotic prescribing

Point-of-care CRP testing has been shown to reduce the likelihood of patients with symptoms of a RTI being prescribed an antibiotic at the index consultation, i.e. the first time they present to a clinician with symptoms. A meta-analysis of 13 studies examining prescribing rates for patients who had been diagnosed with an upper or lower RTI found that the use of point-of-care CRP testing significantly reduced antibiotic prescribing at the index consultation.³ Overall, 44% of patients with a RTI who received point-of-care CRP testing were prescribed an antibiotic at the first consultation, compared with 63% of those who did not undergo CRP testing.³ Among the patients who returned for a follow-up consultation, those who had received point-of-care CRP testing were somewhat less likely to receive a subsequent prescription for an antibiotic. In the 28 days following the index consultation, 32% of patients who underwent CRP testing received an antibiotic, compared to 38% of patients who did not have CRP testing. This difference was not, however, statistically significant.³

Presently there are no data available to measure the effect of point-of-care CRP testing on clinical outcomes in patients with RTIs.

A combination approach including effective communication is best for reducing antibiotic prescribing for patients with RTIs

Both diagnostic uncertainty and non-clinical patient factors, including patient expectations of a prescription, can influence a clinician’s decision to prescribe antibiotics, and the ability to achieve evidence-based prescribing. A study based in general practice in the Netherlands randomised patients with symptoms of a lower RTI to receive point-of-care CRP testing, enhanced communication about their illness, a combination of CRP and enhanced communication or usual care. The clinicians received training in point-of-care testing and enhanced illness-based communication skills. The results showed that:⁴

• Both point-of-care CRP testing and illness-focused communication training resulted in decreased antibiotic prescribing for lower RTIs, with patient recovery and satisfaction reported to not be compromised
• The greatest reduction in antibiotic prescribing for lower RTIs occurred for general practitioners who were able to use both approaches

This suggests that point-of-care CRP testing allows clinicians to have more confidence in their decision of whether to prescribe an antibiotic for a patient with a RTI. However, effective communication with patients about the natural progression of symptoms in a RTI and the role of antibiotics is also an essential element in achieving best outcomes.