Point-of-care CRP testing may help primary care clinicians to identify with more certainty which patients with features of respiratory tract infection do not require antibiotics, therefore reducing the use of antibiotics.
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- Elevated CRP is a marker for bacterial infection and other pathological processes
- Point-of-care CRP testing may be useful for “ruling out” pneumonia in patients with lower RTI symptoms
- Point-of-care CRP testing when symptoms suggest an upper RTI
- Point-of-care CRP testing has been shown to reduce initial antibiotic prescribing
- A combination approach including effective communication is best for reducing antibiotic prescribing for patients with RTIs
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Everyday throughout New Zealand, multiple patients will present to general practice with symptoms of a respiratory tractinfection (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 missa 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-reactiveprotein (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 clinicalscenarios:
- Identifying patients with symptoms of a lower RTI who are unlikely to have pneumonia, i.e. where an antibioticis not appropriate
- Providing patients with an upper RTI who are convinced they “need” an antibiotic with reassurance that a prescriptionfor 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, traumaor infarction.1 The serum CRP level in a “healthy” person is usually less than 5 mg/L; this will begin torise four to eight hours after tissue is damaged, peak within 24 – 72 hours, and return to normal two to three days afterthe pathological process has ceased.1 Bacterial infections of the respiratory tract generally cause a greaterCRP elevation than viral infections.
Health professionals in primary care who are appropriately trained in the use of the point-of-care device can obtainCRP results that, for the purposes of testing a patient with a RTI, are comparable to conventional laboratorytesting (see: “Point-of-care CRP testing is rapid but is it accurate?”). Point-of-care testinghas the advantage of being able to provide the clinician with a CRP result immediately, which can be factoredinto 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 byproviding 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 recommendingthat point-of-care CRP testing may be useful to guide antibiotic prescribing for patients without a clinical diagnosisof pneumonia but with symptoms of a lower RTI, e.g. cough and at least one of: fever, sputum production, wheeze, or chestdiscomfort. 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 unlikelyto have pneumonia
- Antibiotic treatment should be routinely offered to patients with symptoms of a lower RTI and a CRP level > 100mg/L, as they are more likely to have pneumonia, assuming no underlying condition such as malignancy or autoimmune diseaseis present
In patients with symptoms of a lower RTI of uncertain origin and a CRP level between 20 – 100 mg/L the need for antibioticsremains 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 inwhom the consequences of pneumonia could be more severe, a prescription for an antibiotic at the initial consultationmay be a reasonable strategy, while in lower risk patients a delayed prescription may be considered, i.e. to be collected/filledif 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-careCRP testing is in helping to reassure patients that they do not require an antibiotic, if the CRP result supports thisjudgement. A CRP level < 10 mg/L suggests that a patient does not have a bacterial infection and therefore a prescriptionfor an antibiotic is likely to do more harm than good,1 i.e. the potential adverse effects of the antibioticoutweigh 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 prescribedan antibiotic at the index consultation, i.e. the first time they present to a clinician with symptoms. A meta-analysisof 13 studies examining prescribing rates for patients who had been diagnosed with an upper or lower RTI found that theuse 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-upconsultation, those who had received point-of-care CRP testing were somewhat less likely to receive a subsequent prescriptionfor an antibiotic. In the 28 days following the index consultation, 32% of patients who underwent CRP testing receivedan antibiotic, compared to 38% of patients who did not have CRP testing. This difference was not, however, statisticallysignificant.3
Presently there are no data available to measure the effect of point-of-care CRP testing on clinical outcomes in patientswith 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, caninfluence a clinician’s decision to prescribe antibiotics, and the ability to achieve evidence-based prescribing. A studybased in general practice in the Netherlands randomised patients with symptoms of a lower RTI to receive point-of-careCRP 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 resultsshowed that:4
- Both point-of-care CRP testing and illness-focused communication training resulted in decreased antibiotic prescribingfor 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 ableto use both approaches
This suggests that point-of-care CRP testing allows clinicians to have more confidence in their decision of whetherto prescribe an antibiotic for a patient with a RTI. However, effective communication with patients about the naturalprogression of symptoms in a RTI and the role of antibiotics is also an essential element in achieving best outcomes.
Point-of-care CRP testing is rapid but is it accurate?
Point-of-care CRP devices use an enzyme-linked reaction to measure the CRP concentration in a finger-prick blood sample.Manufacturers claim that sample collection and analysis can be performed within two to three minutes by operators trainedin the use of the device.
A systematic review of the attitudes of primary care clinicians to point-of-care testing identified that concern abouttest accuracy was a barrier to implementation into practice.5 A study sponsored by one manufacturer comparedthe performance of CRP point-of-care testing with laboratory-based testing and found that for venous and capillary bloodsamples there was a mean difference of CRP of 1 mg/L when compared with laboratory testing.6
Quality assurance is important with all point-of-care tests so that clinicians have confidence when they are interpretingresults. It is recommended that staff training activities be discussed with any supplier before a point-of-care CRP testingdevice is purchased. Periodic external quality control arranged with a local diagnostic laboratory also ensures that testingaccuracy is maintained.
Acknowledgement
Thank you to Associate Professor Mark Thomas, Infectious Diseases Specialist, University of Auckland and Auckland DHB, Dr Chris Hewison, Clinical Microbiologist, MedLab Central, Dr Rosemary Ikram, Clinical Microbiologist, Christchurch and Dr Cam Kyle, Clinical Biochemist, Auckland for expert review of this article.
References
- Kyle C (Ed). Pathology handbook: a guide to the interpretation of pathology tests. New South Wales: Sonic Healthcare, 2014.
- National Institute for Health and Care Excellence (NICE). Pneumonia - diagnosis and management of community- andhospital-acquired pneumonia in adults. NICE, 2014. Available from: www.nice.org.uk (Accessed Jun, 2015).
- Huang Y, Chen R, Wu T, et al. Association between point-of-care CRP testing and antibiotic prescribing in respiratorytract infections: a systematic review and meta-analysis of primary care studies. Br J Gen Pract 2013;63:e787–94.
- Cals J, Butler C, Hopstaken R, et al. Effect of point of care testing for C reactive protein and training in communicationskills on antibiotic use in lower respiratory tract infections: cluster randomised trial. BMJ 2009;338:b1374.
- Jones CH, Howick J, Roberts NW, et al. Primary care clinicians’ attitudes towards point-of-care blood testing:a systematic review of qualitative studies. BMC Fam Pract 2013;14:117.
- Seamark DA, Backhouse SN, Powell R. Field-testing and validation in a primary care setting of a point-of-care testfor C-reactive protein. Ann Clin Biochem 2003;40:178–80.
