OBJECTIVE: To assess whether the frequency of antibiotic prescriptions to patients with respiratory infections is reduced when general practitioners (GPs) use a C-reactive protein (CRP) rapid test in support of their clinical assessment, and to study whether using the test will have any effect on the course of disease

DESIGN: Randomised controlled trial.

SETTING: 35 general practices, County of Funen, Denmark.

PATIENTS: 812 patients with respiratory infection.

MAIN OUTCOME MEASURES: Frequency of antibiotic prescriptions and morbidity 1 week after the consultation, as stated by the patients.

RESULTS: In the CRP group the frequency of antibiotic prescriptions was 43% (179/414) compared with 46% (184/398) in the control group (odds ratio (OR) = 0.9, NS). After 1 week, increased or unchanged morbidity was stated more frequently in the CRP group (12%) than in the control group (8%) (OR = 1.6, p = 0.05). In the control group, the variable having the greatest influence on whether the GP prescribed antibiotics was the patients' general well-being (OR = 2.9, p < 0.0001), whereas in the CRP group the CRP value had the greatest influence (OR = 1.1 per unit increase (mg/l), p < 0.0001).

CONCLUSION: Based on the present study, the use of the CRP rapid test in support of a possible antibiotic treatment for respiratory infections in general practice cannot be recommended.