CRP Test Guides Antibiotic Prescribing for Respiratory Tract Infections

Fran Lowry

March 23, 2010

March 23, 2010 — C-reactive protein (CRP) testing done in the office to identify inflammation or infection in the body may help physicians determine which patients with respiratory tract infection will benefit from antibiotic treatment, and so reduce unnecessary antibiotic use, according to a new study published in the March/April issue of the Annals of Family Medicine.

"Antibiotics are only beneficial for subgroups of patients with acute lower respiratory tract infections (LRTI) and rhinosinusitis in family practice, yet overprescribing for these conditions is common," write Jochen W. L. Cals, MD, PhD, from Maastricht University, Maastricht, the Netherlands, and colleagues. "Signs and symptoms are of limited value in identifying those patients in need of antibiotic treatment for these conditions."

Uncertainty about the diagnosis and patient expectations and pressure can often prompt family physicians to prescribe antibiotics that are not justified, the study authors write.

The goal of this study was to see whether CRP testing at the time of the office visit would help the physician triage patients into no prescription, delayed prescription, or immediate prescription categories, without compromising their outcomes.

To do so, the investigators randomly assigned 107 patients with LRTI and 151 patients with sinus infections to testing with CRP vs no testing. The patients were recruited from 33 family physicians working in 11 family practice centers in the southeastern part of the Netherlands from November 2007 until April 2008.

The researchers carried out the CRP analysis using QuikRead CRP analyzers (Orion Diagnostica, Espoo, Finland), and results from the test were available within 3 minutes.

The physicians were advised not to prescribe antibiotics when the CRP test results were less than 20 mg/L, to give immediate antibiotics when the results were greater than 100 mg/L, and to consider writing a prescription for delayed antibiotics when the CRP levels were between 20 and 99 mg/L. However, they were free to deviate from this proposed prescribing plan at any time.

The primary outcome was antibiotic use after the index consultation. Secondary outcomes included antibiotic use during the 28-day follow-up, patient satisfaction, and clinical recovery.

The investigators found that patients in the CRP group used fewer antibiotics (43.4%) than patients in the control group (56.6%) after the index consultation (relative risk [RR], 0.77; 95% confidence interval [CI], 0.56 - 0.98).

This difference remained significant during the follow-up period (52.7% vs 65.1%; RR, 0.81; 95% CI, 0.62 - 0.99).

Moreover, in the CRP group, delayed prescriptions, or prescriptions written under the condition that they were not to be used immediately but only if symptoms persisted, were filled only in a minority of patients (23%) vs 72% in the control group (P < 0.001).

The researchers also found that patient satisfaction with care was higher when CRP testing was used during the office visit (P = .03).

Both groups had similar recovery rates.

A limitation of the study is that it was not powered to detect differences between patients with respiratory tract infections and rhinosinusitis. Another is that physicians were not blinded because they needed to know patients' CRP results to decide on appropriate clinical management.

The study authors conclude that point-of-care CRP testing can assist clinicians in making decisions about prescribing, or delaying prescribing, antibiotics. Importantly, they write, such testing may help decrease inappropriate antibiotic use and also increase patient satisfaction without compromising recovery.

Asked to comment on this study by Medscape Family Medicine, Mark T. Gladwin, MD, chief of the Division of Pulmonary, Allergy and Critical Care Medicine at the University of Pittsburgh Medical Center, Pittsburgh, Pennsylvania, said that a similar approach to identifying patients at higher risk of having a bacterial infection or a more severe bacterial infection has been used in many studies using another marker called procalcitonin.

"Using these markers and decision protocols, the investigators were able to reduce the percentage of people who received antibiotics. While the percentage of patients that do not receive antibiotics is only modestly reduced, these strategies may help reduce our current high use of antibiotics for viral upper respiratory illnesses in the US," he said. "Larger studies will be needed to confirm the generalizability of these approaches and to show that these approaches reduce the development of antibiotic resistance."

This study was funded by Orion Diagnostica (Finland), which is the maker of the QuikRead point-of-care CRP testing device.

Dr. Cals is supported by a grant of the Netherlands Organization for Health Research and Development. One of the study authors (Rogier M. Hopstaken, MD, PhD) has disclosed financial relationships with Axis-Shield (Norway) and Orion Diagnostica (Finland).

Ann Fam Med. 2010;8:124-133. Abstract