Unnecessary prescription of antibiotics contributes to the development of treatment-resistant strains. Antimicrobial resistance comes with high morbidity and mortality burden, especially for future generations, with potential high impact on healthcare costs. Efficient strategies are therefore needed to limit overuse of antibiotics. This paper investigates the cost-effectiveness of screening patients suffering from lower tract inflammation with procalcitonin or lung ultrasonography, two diagnostic tools that help detect the presence of a bacterial infection, therefore guiding antibiotic prescription decisions. The clinical effectiveness of these strategies has been demonstrated in the primary care setting (lhopitallier 2021), but evidence is needed on the cost-effectiveness of these options. We used data from a cluster-randomized multicenter clinical trial conducted in Switzerland and estimated patient-level costs using data on resource use to which we applied Swiss tariffs. By combining the incremental costs of the two treatments and the reduction in the 28-day antibiotic prescription rate (APR) compared to usual care, we calculated incremental cost-effectiveness ratios (ICER). We also used the cost-effectiveness acceptability curve as an analytical decision-making tool. The robustness of the findings is ensured by probabilistic sensitivity analysis and by scenario analysis. In the base case scenario, the icer with respect to usual care is 2.2 Swiss francs (CHF) per percentage point reduction in antibiotic prescription for the procalcitonin-treated group, while it is 4.2 for the ultrasonography group. This is because, despite similar clinical effectiveness, the incremental cost of the ultrasound group is almost double that of procalcitonin. Furthermore, we found that for a willingness to pay per patient more than 2 CHF per percentage point reduction in the APR, procalcitonin is the strategy with the highest probability to be cost-effective. Our findings suggest that testing patients with respiratory symptoms with procalcitonin to guide antibiotic prescription in the primary care setting represents good value for money.