Factors associated with C-reactive protein testing when prescribing antibiotics in general practice: a register-based study

Background: The use of C-reactive protein (CRP) tests has been shown to safely reduce antibiotic prescribing for acute respiratory tract infections (RTIs). The aim of this study was to explore patient and clinical factors associated with the use of CRP testing when prescribing antibiotics recommended for RTIs. Methods: A nation-wide retrospective cross-sectional register-based study based on first redeemed antibiotic prescriptions issued to adults in Danish general practice between July 2015 and June 2017. Only antibiotics recommended for treatment of RTIs were included in the analysis (penicillin-V, amoxicillin, co-amoxicillin or roxithromycin/clarithromycin). Logistic regression models were used to estimate odds ratios for patient-related and clinical factors on performing a CRP test in relation to antibiotic prescribing. Results: A total of 984,149 patients redeemed at least one antibiotic prescription during the two-year period. About half of these prescriptions (49.6%) had an RTI stated as the indication, and a CRP test was performed in relation to 45.2% of these scripts. Lower odds of having a CRP test performed in relation to an antibiotic prescription was found for patients aged 75 years and above (OR 0.82, 95CI 0.79–0.86), with a Charlson Comorbidity Index of more than one (OR 0.93, 95CI 0.91–0.95), unemployed or on disability pension (OR 0.84, 95CI 0.83–0.85) and immigrants (OR 0.91, 95CI 0.88–0.95) or descendants of immigrants (OR 0.90, 95CI 0.84–0.96). Living with a partner (OR 1.08, 95CI 1.07–1.10), being followed in practice for a chronic condition (OR 1.22, 95CI 1.18–1.26) and having CRP tests performed in the previous year (OR 1.78, 95CI 1.73–1.84) were associated with higher odds of CRP testing in relation to antibiotic prescribing. Conclusions: Differences were observed in the use of CRP tests among subgroups of patients indicating that both sociodemographic factors and comorbidity influence the decision to use a CRP test in relation to antibiotic prescriptions in general practice. Potentially, this means that the use of CRP tests could be optimised to increase diagnostic certainty and further promote rational prescribing of antibiotics. The rationale behind the observed differences could be further explored in future qualitative studies.